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2024 GMC Sierra 2500 HD, 6.6L L8T gas, Allison 10-speed. Currently about 30,000 miles. Truck has had an easy life. I’ve towed maybe a couple hundred miles total since new. No heavy towing yet. On the highway it suddenly bucked hard, then immediately downshifted and stayed in 2nd. Felt like I slammed on the brakes with traffic behind me. I had to limp it at about 45 mph at 4500 rpm to the nearest exit. Transmission temp climbed quickly to 190°F before I shut it off, which is the hottest I’ve ever seen it (still not that hot). This was the first time the check engine light came on. After restarting it, I drove it about an hour to the dealer afterward taking only backroads. Dealer says they don’t know what’s wrong and that all the codes are historical. One of the techs looked at it while I was grabbing my stuff and said “this ain’t good.” They’re doing a test drive tonight and said they’ll consult their technical specialist. Has anyone else had this on a low-mileage L8T / 10L1000? Did GM actually fix it with the valve body TSB? Considering it was driving absolutely fine when this happened, I really don't trust the truck and its looking like the dealer isn't going to do anything about it.

Nice! What made you want to trade up your '25? with the 3.0 for a new one? (As I look suspiciously at mine...)

Figured I'd at least get this section going. I'll be trading a 2025 GMC Sierra 1500 3.0l in on a GMC Yukon with the 3.0l Duramax.

Well, that's a lot of info - Thanks, but I think I'll stick to that old but wise saying, " If it ain't broke, don't fix it".

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Bots post VIN numbers? That was meant for the GMCustomerService since they don't allow direct messaging. Thanks for playing

Smoke test the system. You can buy a cheap smoke machine from Amazon and within a few minutes if there's any leaks then you find the problem if there's no leaks you have two choices. Trace it out for electrical issues or replace everything and then see what happens. I'm about to replace everything thanks to the previous owner butchering all the lines under the truck.

Best to use to clean out an engine and after 3-4 OCI's go back to the HM Oils. People seem to think if the oil isn't Dexos approved then it's not a good oil. Dexos is just a certification GM requires and the oil companies have to pay for that certification. With the shortage of oils from the foreign countries a lot of Oil makers are having to remove the Dexos certification.

I've been under the truck several times but it still has the same original parts minus the tubes as the previous owner cut it all out and used cheap gas line hose and it is soft and any movement causes it to pinch or kink and stops vapors from moving through the system. Trying to find someone who installed the updated relocation kit and which one of those two they used. Prefer not to use rubber hose where it's not needed.

Yah, I found a leak on the condenser, replaced that and the other replacement parts, re-charged, good to go. thank you.

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Thanks for that, yes just because I could I measured what came out just to give me some guidance although I already knew to expect it to take at least 9.5 to just throwing in the whole 10 quarts off the shot and doing a one and done heat cycle to drop out the excess to get to the proper level. I don't recall exactly now what I measured that came out but was less than I put back in, I knew I spilled some on the garage floor but the main part was that I was thrilled in the discovery I did not have to touch my exhaust to flex it down. The gasket manipulating is a pain of course to create that clearance to take the pan out and put back in but its all very doable if one is careful and not forcing the gasket to flex too much. From the quote I got at a transmission shop of 900.00 here in Canada ( never asked at the dealer what they charge ) I saved 700.00 doing it myself after paying for the supplies so that to me paid very good wages !, and I knew what fluid was put in and that I had changed the filter and that the level is correct without any doubts.

I do have one of the AFM diasable box, using it for last 1.5 years.

I found a setup that lets me open the cover partway with racks installed, using side-rail-mounted systems for easy access.

Typically its said and I agree so far that the engine oil drain plug oring is not required to be changed out unless you see some damage happening to the oring as apparently the oring lasts well. The dealer I have been getting a few parts from never even stocked the oring but instead stocked the whole drain plug that comes with a new oring which for the dealer is easier because they just throw in a new drain plug if there was any question about damage on it as well and charge the customer accordingly but again only if it is needed. Also a hint about the drain plug oring to help it last vs a risk of causing damage to it, after its been removed and wiped off or washed off ( that is a whole other topic about some solvents damaging orings because some solvent types do ) to make sure to relube the oring with a bit of new oil so that it won't "grip" on the sealing surface of the pan and needlessly stress out the oring. Its no different than putting some oil on the sealing ring of the engine oil filter. So I just grabbed a new drain plug to have on hand although more recently bought just the oring as well but as its special it costs half the price of the drain plug ... ! Since you mentioned the hate to be empty handed theme, I am not sure what you have in the way of filter removal tools as I like using the exact sized for the filter steel 1" wide band with side to side swivel handle filter removal tool, and it can be used to snug up the filter without risk of damaging a filter as well ( its probably a lisle brand I have ). The drain plug hex size is 15mm and I always like using a 6 point socket if I have a choice and with this truck I've been using just a 3/8 ratchet that has a fairly long handle. Do you have a funnel that will work to pour oil in as that is definitely the short coming bastard part about the design with that fill port on the valve cover on such an angle that no normal funnel will even work. There are adapters and things on the market that will set into or screw into that fill port, I didn't want to deal with US shipping as that is all I was seeing at the time so caved and bought a Lisle brand multi vehicle fit adapter funnel kit and it really works well but there are much less expensive adapters out there that work in conjunction with an off the shelf funnel that would do the job also. Now that I have it, I like how it works and works so slick with the shape of the Amsoil 1 quart containers I have now switched over to. Whatever you do, have a funnel system of some sort as you will be swearing if you dropped the oil and then realize you have nothing to properly pour new oil in without spilling it all over the engine !. Other comments, quite a bit of oil flows out down the filter when its cracked loose due to the housing above the filter so let it dribble down the filter until it slacks off flow and then remove the filter to create less possible mess. It seems these engines can sit for quite a while and drip and if you have time let it sit there and drip out of the engine as much as it wants. Also a good time to grease the 9 zerks on the front end, that's my typical practice anyway to grease the suspension and steering each time I change the oil. And remember to reset the oil change minder ( not something I am used to doing with older vehicles and equipment ).

I really did not measure what came out. I carefully followed directions to check level after i did the spill and fill and filter change. I used 10 quarts. 9 was not quite enough. My trans temp was about 175 when I checked it. Truck sitting in my driveway very close to level where I always check oil pretty much every time for consistency. My driveway is just ever so slightly downhill to run water to the street.

Sounds like maybe it's announcing Navigation turns or Alerts (it mutes the music) ? When it mutes again, turn up the volume quickly and see if maybe the navigation volume is really low?

If you were a classic car you would be a retro ride Thank goodness for modern medicine.

Kroger by me is still $5.06. It's as high as $5.90 (regular/87) at some other nearby stations but they're always high as balls...I'm not sure how they stay in business. Diesel? If you have to ask, you can't afford it...

Argh ... I prefer crush washer but a big big thank you JR !!!

There is no crush washer. The seal is part of the plug and is intended to be reusable. After six oil changes mine is still fine. Same plug part number is on my 2021. It looks like this:

I use Amsoil products, it's not overpriced trash IMO.

Hey , I need to know before my first oil change so I’m not caught empty-handed—does the drain plug on the 2025 6.6 gas use a crush washer or a rubber seal O-ring on the plug itself? thanks

3.49 Kroger’s in Montgomery Tx. Going down still not the cheapest in my area. With my discount I paid 3.39.