Gas mileage when towing 8k lbs.

Jettech1 · November 25, 2025

Lots of people out there are wondering, I'm guessing a lot of diesel owners. I could be wrong about that but here's the scoop. We towed our 8k lb camper from Alabama to Maine not long ago with our 6 speed 22 custom model 2500. Got 9mpg with the cruise set on 65. The only time I would use tow mode is when we were in heavy traffic or around town. Aside from that, I would turn it off and just let it do its thing. Going over the Pocono's it would drop down to 4th gear at times but 99% of the time, 5th gear would take care of keeping us at speed. Trans temps never exceeded 204. The reason I used tow mode while in traffic or around town is because it would hold the gear longer and not try to hit the next one. 8k lbs isn't even close to what our trucks are capable of. But most campers, if they are not a fifth wheel don't weigh that much. So these trucks are amazingly efficient and will get the job done with no extra thought or maintenance. Those of you that have the 10 speeds I have heard both positive and negative stories. I wish you all the best and hope you have a million miles of smiles!!

Edited November 25, 2025 by Jettech1

newdude · November 25, 2025

I had the "pleasure" (not really but I got paid so I guess I can't complain) of towing about 7000lbs of boat and trailer for the bossman at work 4 times this year. 3 of the 4 times I got to use a 2024 HD 6.6 with 10 speed. The 4th time was a 2015 6.0 6 speed.

The 6.6/10 speed got 10mpg every single time towing it. Never measured the old 2015 truck. But. What a driving difference between the two of those. The 6.6/10 speed made easy work of that boat for sure. Got up to 55-60mph quite good as well. That old 6.0 was working HARD towing the same boat. Its amazing what 41hp and 84ft.lbs of torque and a way better tuned powerband can accomplish. Oh, and the 10 speed with 3.73 vs the 6L90 and 4.10s. That 6.6/A10 felt like you were pulling it with an LMM or LML Duramax.

asilverblazer · November 25, 2025

I posted this recently:

My 1999 1/2 ton 4.8 2wd, 1999 1/2 ton 5.3 4x4, 2007 1/2 ton 5.3 4x4, 2015 1/2 ton 5.3 4x4, 2016 1/2 ton 6.2 4x4 and my 2018 1 ton diesel 4x4 all get 9 mpg towing:

Large pontoon boat

2 horse trailer

3 horse trailer

27' travel trailer

35' travel trailer

16' utility trailer with tractor, loader and implements

22' gooseneck car hauler with cars

16' utility trailer with hay

My Dad's GM's and father in laws Fords all do the same too.

Jettech1 · November 25, 2025

28 minutes ago, asilverblazer said:

I posted this recently:

My 1999 1/2 ton 4.8 2wd, 1999 1/2 ton 5.3 4x4, 2007 1/2 ton 5.3 4x4, 2015 1/2 ton 5.3 4x4, 2016 1/2 ton 6.2 4x4 and my 2018 1 ton diesel 4x4 all get 9 mpg towing:

Large pontoon boat

2 horse trailer

3 horse trailer

27' travel trailer

35' travel trailer

16' utility trailer with tractor, loader and implements

22' gooseneck car hauler with cars

16' utility trailer with hay

My Dad's GM's and father in laws Fords all do the same too.

That 9mpg is weird. Diesel or gas. For some reason that 9mpg is very common.

asilverblazer · November 26, 2025

23 hours ago, Jettech1 said:

That 9mpg is weird. Diesel or gas. For some reason that 9mpg is very common.

Technically it takes X amount of energy to Y amount of work, the only thing that changes is the efficiency in the system. At a certain point that efficiencies effect is lost. To my knowledge an 80000 18-wheeler is getting 6ish. Compared to me at 16000 getting 9 and at 8800 (unloaded) getting 18-20. If you charted that 'curve' it would less like a curve and more like a wall or cliff.

There are only so many units of energy in each drop of fuel whether its gas or diesel.

Edited November 26, 2025 by asilverblazer

Jettech1 · November 26, 2025

2 hours ago, asilverblazer said:

Technically it takes X amount of energy to Y amount of work, the only thing that changes is the efficiency in the system. At a certain point that efficiencies effect is lost. To my knowledge an 80000 18-wheeler is getting 6ish. Compared to me at 16000 getting 9 and at 8800 (unloaded) getting 18-20. If you charted that 'curve' it would less like a curve and more like a wall or cliff.

There are only so many units of energy in each drop of fuel whether its gas or diesel.

Have you seen those tractor trailers weighing in at 80k getting 11mpg? Yeah truth. Now figure that one out. Do the math on that one buddy and let me know your results...

Edited November 26, 2025 by Jettech1

KARNUT · November 26, 2025

All my trucks 7.3,5.9 diesel V-10 gas got 7 MPG. The trailer and equipment were the same. The diesels from 45 MPH to 65 stayed in fourth gear. The V-10s could down shift at 60 MPH to 3rd to maintain speed. The diesels couldn’t. I stopped pulling equipment in 1999. My equipment had cabs wind drag was a determining factor. Overdrive wasn’t an option.

dieselfan1 · November 27, 2025

Throw in a 20 mph wind what do you get for mpg?

dieselfan1 · November 27, 2025

I actually got 9mpg recently towing my 6x12 cargo trailer now that I think about it.

I haven’t towed anything else yet.

KARNUT · November 27, 2025

31 minutes ago, dieselfan1 said:

Throw in a 20 mph wind what do you get for mpg?

Hey, Mr confused individual. You would get less. Hope that helps your confusion.

Jettech1 · December 2, 2025

On 11/24/2025 at 9:14 PM, newdude said:

I had the "pleasure" (not really but I got paid so I guess I can't complain) of towing about 7000lbs of boat and trailer for the bossman at work 4 times this year. 3 of the 4 times I got to use a 2024 HD 6.6 with 10 speed. The 4th time was a 2015 6.0 6 speed.

The 6.6/10 speed got 10mpg every single time towing it. Never measured the old 2015 truck. But. What a driving difference between the two of those. The 6.6/10 speed made easy work of that boat for sure. Got up to 55-60mph quite good as well. That old 6.0 was working HARD towing the same boat. Its amazing what 41hp and 84ft.lbs of torque and a way better tuned powerband can accomplish. Oh, and the 10 speed with 3.73 vs the 6L90 and 4.10s. That 6.6/A10 felt like you were pulling it with an LMM or LML Duramax.

You were the one who new the differences between the gas and diesel 10L1000 trans right from the beginning. Most people didn't. Now chevy is paying the price, not just for slapping a sticker on it calling it an Allison, but also with longevity. I was tempted to upgrade to the 10 speed but loved my 6 speed so much and its reliable history that I didn't upgrade. I think dodge finally went with a winner using the ZF 8 speed. I had that "version" we will say trans in my 2016 Dodge Charger SRT and it was to die for. But, I have the Ford 10 speed in our 25 Explorer and love it!! I get that our Explorer nor our charger is an HD truck that requires a lot more "beef" in durability. But I do think Dodge just got a step above everyone else using the ZF. Time will tell when it comes to endurance and reliability.

newdude · December 2, 2025

1 hour ago, Jettech1 said:

You were the one who new the differences between the gas and diesel 10L1000 trans right from the beginning. Most people didn't. Now chevy is paying the price, not just for slapping a sticker on it calling it an Allison, but also with longevity. I was tempted to upgrade to the 10 speed but loved my 6 speed so much and its reliable history that I didn't upgrade. I think dodge finally went with a winner using the ZF 8 speed. I had that "version" we will say trans in my 2016 Dodge Charger SRT and it was to die for. But, I have the Ford 10 speed in our 25 Explorer and love it!! I get that our Explorer nor our charger is an HD truck that requires a lot more "beef" in durability. But I do think Dodge just got a step above everyone else using the ZF. Time will tell when it comes to endurance and reliability.

On the whole Allison thing, I don't know why GM just didn't pay Allison for the entire project, be it an 8 or 9 or 10 speed (whatever they'd have come up with). Instead, GM stuck to their guns on the joint venture 10 speeds with Ford, and BOTH brands are feeling the hurt now. The 10R140 has many of the same problems the 10L1000 has.

newdude · December 3, 2025

20 hours ago, Jettech1 said:

You were the one who new the differences between the gas and diesel 10L1000 trans right from the beginning. Most people didn't. Now chevy is paying the price, not just for slapping a sticker on it calling it an Allison, but also with longevity. I was tempted to upgrade to the 10 speed but loved my 6 speed so much and its reliable history that I didn't upgrade. I think dodge finally went with a winner using the ZF 8 speed. I had that "version" we will say trans in my 2016 Dodge Charger SRT and it was to die for. But, I have the Ford 10 speed in our 25 Explorer and love it!! I get that our Explorer nor our charger is an HD truck that requires a lot more "beef" in durability. But I do think Dodge just got a step above everyone else using the ZF. Time will tell when it comes to endurance and reliability.

I haven't been on their website in a while, and its funny that I suggested a 9 speed as one of my gear count options...

9-Speed Transmission | Allison Transmission

Allison makes their own 9 speed. And it only weighs about 20-30lbs more than the 10L1000.

But. Its in the 2000 series transmission so it doesn't have a park pawl like the 1000 series can have. I'm sure that could be fixed though for pickup use.

The brochure which has the gear ratio charts - 9-Speed-Brochure.pdf

The fact that this exists tells me GM should have worked with Allison on making a pickup version of this and not go at it themselves and then just pay Allison for their name.

Edited December 3, 2025 by newdude