10L1000 anyone with High Mileage ? I hate Damocles....

BuckWallace · February 1

3 hours ago, Byrds8 said:

Yeah I feel you. I think I’ll bring this up and tell them we will be waiting on doing anything since it shifts fine. Unless they can produce something saying it shouldn’t be. That TSB didn’t seem to allude to doing anything.

On a side note, I want them to replace my driver side mirror again. They recently replaced it to stop a whistle. Now it tastes 2-3 seconds longer to fold than the passenger side. Figure Ill get a good one eventually lol

Ha, I had my driver side mirror replaced last year due to excessive shaking (sounds like another common issue). It, too, closes slower than the passenger side, but maybe only by ~1 second. Hopefully the parts lottery is kind to you this time.

Byrds8 · February 1

I could handle 1 second. The amount of time it is right now is just too much considering it’s a $75K truck. They may tell me to pound sand though. We shall see.

Homer1959 · February 1

1 minute ago, BuckWallace said:

Ha, I had my driver side mirror replaced last year due to excessive shaking (sounds like another common issue). It, too, closes slower than the passenger side, but maybe only by ~1 second. Hopefully the parts lottery is kind to you this time.

Is it shaking less

Homer1959 · February 1

20 minutes ago, Homer1959 said:

Is it shaking less

Yessss thanks

BuckWallace · February 1

37 minutes ago, Homer1959 said:

Is it shaking less

Yes, the new one is definitely shaking way less.

Chuck FB · February 5

I see as of today its official that GM will pick up where they left off with once again being able to use the Allision branding collaboration. So with that said our transmissions are great again .

If only there had been a proper joint venture from the ground up with the 10L1000 to have prevented design and material short comings and had created a truly bullet proof transmission in the first place.

asilverblazer · February 5

4 hours ago, Chuck FB said:

I see as of today its official that GM will pick up where they left off with once again being able to use the Allision branding collaboration. So with that said our transmissions are great again .

If only there had been a proper joint venture from the ground up with the 10L1000 to have prevented design and material short comings and had created a truly bullet proof transmission in the first place.

I saw the news on that and was thoroughly insulted at the marketing speak garbage they spewed out on it. We ALL know how much Allisons involvement in the 10L1000 was and we ALL know how superficial the emblem was/is. The marketing guys are convinced that the emblem being returned will make us more confident and rely more on our trucks because of it. We KNOW IT IS NOT AN ALLISON transmission and the emblem wasn't fooling anyone, when it was there the first time, when it got removed, and now that its back. The curious aspect I want to know is - how many more trucks is that little emblem going to sell? (Hint: the same amount as that goofy number on the back of the Cadillacs)

0.

Deadwood · July 21

New member here, very long time occasional guest. Saw this thread, thought it would be a good time to contribute someting. It is only my experience and not a claim that everyone will have the same.

I bought my '20 3500 L5P new and have put 99.9% (literally) of it's current ~400k miles on it myself, with over 50% of that towing loads between 4k to 15k, and to me this truck has been nothing short of amazing. For the first 235k I had zero issues, and from there until 321k I replaced a NOx sensor, two failing glow plugs, and three of the notorious injector connectors. I believe this truck is in part, a testament to good luck, but also good care and following a decent maintenance schedule (I also keep meticulous records.) As a result, it looks as good as a well cared for 70k rig, up and down, inside and out.

At some point before that 321k mile mark I began to get a little spooked about the 10L1000, especially the valve body. Word of mouth about potential issues prompted me to jump on the net to sift through all the noise and determine what all the fuss was about. I routinely take long trips, coast-to-coast and points in between, so roadside breakdowns can be '...a thousand miles from nowhere' and a bit of a challenge, and though I had no issues, my guard was up and activated.

And then I stumbled across a chance to salvage some parts off a new 2025 that had been wrecked in transport. I grabbed a few wear items (alternator, pulleys, etc.) and on a whim asked what the ten speeder would cost me. It was cheap...really cheap. I knew some changes had been made in the '24+ version 10L and were supposedly not compatible, but I called service/parts at my local Chevy dealer and asked why and they didn't know. A call to a well known aftermarket transmission outfit revealed it was very likely it would be fine, but to them not 100% sure.

Because it was cheap (really cheap) and I was spooked, I took the chance. Had it installed by a local shop and it worked like a champ, shifted just like the original. At it's first service at 37k, I had the shop put in a Next Gen valve body kit, which after some initial hiccups and rough shifts, smoothed out though with somewhat firmer shifting.

All that said, I have a very serious concern about my newer transmission as just two weeks ago it suddenly began to exhibit a strong reluctance to engage forward or reverse. It was a bit past due anyway so I took it in for service. The reason it was sticking was due to 'glitter' in the fluid clogging the filter...not good folks, often indicates a converter giving out. We ended up going ahead with the new filter and fluid, first to see if it would move and shift, and then if so buy me a little time. It did, and I've driven it over a thousand miles and it is shifting smooth, no noises or slipping. Regardless, it looks like a third gearbox is in my future so I can resume taking long trips with some confidence. In the very short term, my curiosity will have me examining the fluid to check how much glitter has reappeared.

An earlier poster had alleged, in the context of 10L100 failures, that it is another example of how we seasoned citizens somehow descend into hysteria, lose control of our senses, and react irrationally after brief encounters with the idiocy of the internet infosphere. Let me say (and I have used and abused said internet since it's infancy) there is no segment of the populace that has a corner on over-reaction to digital garbage. Just as my offering of experience in this arena is purely anecdotal and should not be considered gospel or all-encompassing, I believe it is still worthwhile information to consider, along with other relevant anecdotal experiences about things like complex transmissions, especially when balanced with other sources.

So to answer the original question, yes I got high miles out of my first 10L, trouble free for 321,000. Now I really wonder how much longer it would have went. Did I 'overreact' to the internet ghouls by replacing a 'good' one with a 'bad' one? Maybe. Who knows, the thing might have taken a puke a 100 miles later. So I'll just fix it again, then move on and start thinking about all the other stuff that will eventually wear out. It still has the original brakes (they're at ~60%), original injectors/pump, turbo, water pump, etc....pretty much original everything. Knock on wood.

Homer1959 · July 22

5 hours ago, Deadwood said:

New member here, very long time occasional guest. Saw this thread, thought it would be a good time to contribute someting. It is only my experience and not a claim that everyone will have the same.

I bought my '20 3500 L5P new and have put 99.9% (literally) of it's current ~400k miles on it myself, with over 50% of that towing loads between 4k to 15k, and to me this truck has been nothing short of amazing. For the first 235k I had zero issues, and from there until 321k I replaced a NOx sensor, two failing glow plugs, and three of the notorious injector connectors. I believe this truck is in part, a testament to good luck, but also good care and following a decent maintenance schedule (I also keep meticulous records.) As a result, it looks as good as a well cared for 70k rig, up and down, inside and out.

At some point before that 321k mile mark I began to get a little spooked about the 10L1000, especially the valve body. Word of mouth about potential issues prompted me to jump on the net to sift through all the noise and determine what all the fuss was about. I routinely take long trips, coast-to-coast and points in between, so roadside breakdowns can be '...a thousand miles from nowhere' and a bit of a challenge, and though I had no issues, my guard was up and activated.

And then I stumbled across a chance to salvage some parts off a new 2025 that had been wrecked in transport. I grabbed a few wear items (alternator, pulleys, etc.) and on a whim asked what the ten speeder would cost me. It was cheap...really cheap. I knew some changes had been made in the '24+ version 10L and were supposedly not compatible, but I called service/parts at my local Chevy dealer and asked why and they didn't know. A call to a well known aftermarket transmission outfit revealed it was very likely it would be fine, but to them not 100% sure.

Because it was cheap (really cheap) and I was spooked, I took the chance. Had it installed by a local shop and it worked like a champ, shifted just like the original. At it's first service at 37k, I had the shop put in a Next Gen valve body kit, which after some initial hiccups and rough shifts, smoothed out though with somewhat firmer shifting.

All that said, I have a very serious concern about my newer transmission as just two weeks ago it suddenly began to exhibit a strong reluctance to engage forward or reverse. It was a bit past due anyway so I took it in for service. The reason it was sticking was due to 'glitter' in the fluid clogging the filter...not good folks, often indicates a converter giving out. We ended up going ahead with the new filter and fluid, first to see if it would move and shift, and then if so buy me a little time. It did, and I've driven it over a thousand miles and it is shifting smooth, no noises or slipping. Regardless, it looks like a third gearbox is in my future so I can resume taking long trips with some confidence. In the very short term, my curiosity will have me examining the fluid to check how much glitter has reappeared.

An earlier poster had alleged, in the context of 10L100 failures, that it is another example of how we seasoned citizens somehow descend into hysteria, lose control of our senses, and react irrationally after brief encounters with the idiocy of the internet infosphere. Let me say (and I have used and abused said internet since it's infancy) there is no segment of the populace that has a corner on over-reaction to digital garbage. Just as my offering of experience in this arena is purely anecdotal and should not be considered gospel or all-encompassing, I believe it is still worthwhile information to consider, along with other relevant anecdotal experiences about things like complex transmissions, especially when balanced with other sources.

So to answer the original question, yes I got high miles out of my first 10L, trouble free for 321,000. Now I really wonder how much longer it would have went. Did I 'overreact' to the internet ghouls by replacing a 'good' one with a 'bad' one? Maybe. Who knows, the thing might have taken a puke a 100 miles later. So I'll just fix it again, then move on and start thinking about all the other stuff that will eventually wear out. It still has the original brakes (they're at ~60%), original injectors/pump, turbo, water pump, etc....pretty much original everything. Knock on wood.

Thanks for the feedback on my opening post, and wow, that truck has really treated you well.

Chuck FB · July 22

7 hours ago, Deadwood said:

New member here, very long time occasional guest. Saw this thread, thought it would be a good time to contribute someting. It is only my experience and not a claim that everyone will have the same.

I bought my '20 3500 L5P new and have put 99.9% (literally) of it's current ~400k miles on it myself, with over 50% of that towing loads between 4k to 15k, and to me this truck has been nothing short of amazing. For the first 235k I had zero issues, and from there until 321k I replaced a NOx sensor, two failing glow plugs, and three of the notorious injector connectors. I believe this truck is in part, a testament to good luck, but also good care and following a decent maintenance schedule (I also keep meticulous records.) As a result, it looks as good as a well cared for 70k rig, up and down, inside and out.

At some point before that 321k mile mark I began to get a little spooked about the 10L1000, especially the valve body. Word of mouth about potential issues prompted me to jump on the net to sift through all the noise and determine what all the fuss was about. I routinely take long trips, coast-to-coast and points in between, so roadside breakdowns can be '...a thousand miles from nowhere' and a bit of a challenge, and though I had no issues, my guard was up and activated.

And then I stumbled across a chance to salvage some parts off a new 2025 that had been wrecked in transport. I grabbed a few wear items (alternator, pulleys, etc.) and on a whim asked what the ten speeder would cost me. It was cheap...really cheap. I knew some changes had been made in the '24+ version 10L and were supposedly not compatible, but I called service/parts at my local Chevy dealer and asked why and they didn't know. A call to a well known aftermarket transmission outfit revealed it was very likely it would be fine, but to them not 100% sure.

Because it was cheap (really cheap) and I was spooked, I took the chance. Had it installed by a local shop and it worked like a champ, shifted just like the original. At it's first service at 37k, I had the shop put in a Next Gen valve body kit, which after some initial hiccups and rough shifts, smoothed out though with somewhat firmer shifting.

All that said, I have a very serious concern about my newer transmission as just two weeks ago it suddenly began to exhibit a strong reluctance to engage forward or reverse. It was a bit past due anyway so I took it in for service. The reason it was sticking was due to 'glitter' in the fluid clogging the filter...not good folks, often indicates a converter giving out. We ended up going ahead with the new filter and fluid, first to see if it would move and shift, and then if so buy me a little time. It did, and I've driven it over a thousand miles and it is shifting smooth, no noises or slipping. Regardless, it looks like a third gearbox is in my future so I can resume taking long trips with some confidence. In the very short term, my curiosity will have me examining the fluid to check how much glitter has reappeared.

An earlier poster had alleged, in the context of 10L100 failures, that it is another example of how we seasoned citizens somehow descend into hysteria, lose control of our senses, and react irrationally after brief encounters with the idiocy of the internet infosphere. Let me say (and I have used and abused said internet since it's infancy) there is no segment of the populace that has a corner on over-reaction to digital garbage. Just as my offering of experience in this arena is purely anecdotal and should not be considered gospel or all-encompassing, I believe it is still worthwhile information to consider, along with other relevant anecdotal experiences about things like complex transmissions, especially when balanced with other sources.

So to answer the original question, yes I got high miles out of my first 10L, trouble free for 321,000. Now I really wonder how much longer it would have went. Did I 'overreact' to the internet ghouls by replacing a 'good' one with a 'bad' one? Maybe. Who knows, the thing might have taken a puke a 100 miles later. So I'll just fix it again, then move on and start thinking about all the other stuff that will eventually wear out. It still has the original brakes (they're at ~60%), original injectors/pump, turbo, water pump, etc....pretty much original everything. Knock on wood.

Would you mind sharing your maintenance regiment and what brands of oils you have been using. For example engine oil change intervals and the specific type and viscosity used, fuel filter intervals, ( engine coolant, is one that tends not to get changed often enough ) diff oil type and interval, transmission pan drops if that is how you refreshed a portion of the oil, transfer case and anything else you happen to think of.

By the way has the truck been on a lot of salty roads over these years and the first thing that shows up is the wax is gone on the frame from the rear of the transmission back and it isn't typically kind to brake life either which is why I was surprised how fantastic the brake pad life has been. Also if the park brake pads have been replaced as that has been discussed on here as per the rust belt area's cause the park brake shoe linings to fall right off.

KARNUT · July 22

I think the key point to longevity that may be being missed is the way the vehicle is being used. Long operating times with limited cold starts is one. Sustained speeds is another. Vehicles get better fuel mileage on highways for that reason.

Pryme · July 22

I would have kept the new one until I needed it.

c4racer2 · July 23

On 7/22/2026 at 6:24 AM, Pryme said:

I would have kept the new one until I needed it.

same!!

Chuck FB · July 23

On 7/22/2026 at 6:24 AM, Pryme said:

I would have kept the new one until I needed it.

Of course we have the privilege of seeing into the future and noting how the used transmission for whatever reasons did not do so well or so it would appear with the metal wear and its just a matter of when it will pile up. The unknown is the original transmission, how much longer would it have kept going and would it have left him stranded far off somewhere at a time when getting repairs may have been impossible to find. I rather doubt that these 10L1000 transmissions are going to be looked back on as an incredibly long life type of unit as there are other items besides the valve body that were never made as well as they could have been and why the aftermarket has come out with some better grade components. I guess there is one way of finding out though if the original trans is still on the shelf, install it with no modifications and keep on adding on the miles and see how far it will go !.