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Old 12-04-2022, 08:55 AM   #1
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GM 6.6 gasoline engine

Is anyone towing a fifth wheel with GMís 6.6 Gas engine?
Now that it has been available for a few years and with the shortage and high price of diesel. Has anyone switched from diesel to gas?

Would appreciate your comments bad or good.

Thanks
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Old 12-04-2022, 10:37 AM   #2
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My brother has a new Sierra with the 6.6, he loves it. Gets better gas mileage than my 5.3 pulling a slightly heavier trailer! He averages around 12 mpg pulling a 6500 lb trailer.
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Old 12-04-2022, 03:31 PM   #3
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What does he average without a trailer behind?
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Old 12-04-2022, 04:38 PM   #4
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I have '21 Sierra with the 6.6L gas. Rural driving (60 or less, stop signs with few lights) I average about 19 empty. Pulling my TT I am around 8.5 (65-70)unless the winds are real bad. The 274CKDS sits high so LOTS of frontal area.
No issues with power. Didn't want diesel for my daily driving. Happy overall.
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Old 12-04-2022, 05:01 PM   #5
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Originally Posted by Toolguy5 View Post
Is anyone towing a fifth wheel with GM’s 6.6 Gas engine?
Now that it has been available for a few years and with the shortage and high price of diesel. Has anyone switched from diesel to gas?

Would appreciate your comments bad or good.

Thanks
Towing heavy loads I would never switch back to a current gas engine. The last gas engine I owned in a truck was an 2002 8.1 GM 3/4 T and it was a good engine. Very thirsty, but a lot of power. My current Cummins and the last Duramax will out pull that truck, and get a lot better mileage doing it. I've seen no shortage of diesel fuel in my area. High prices, yeah. I paid $5.15 today per gallon. If there was a gas engine that would compare with one of the diesels I've owned, I would switch back immediately. I think if someone is pulling less that 12000 lbs or so, the decisision is up to you. I'm reffering to havy trailers, not my 28.5. I would pull that with a gas motor easily.
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Old 12-05-2022, 07:34 AM   #6
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Thanks to all who replied.

I have always been able to get Diesel but I keep hearing everyone say the reason for the high price is short supply. Most stations here are $5.85 to $5.99 per gallon.I don’t see any signs on price coming down.

I use to tow with a 6.0 gas and experienced over heating. Went to Diesel in 2006 and what a difference. But now that GM has the 6.6 and Ford has the 7.3 I was wondering how the perform.

Thanks again.
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Old 12-05-2022, 09:02 AM   #7
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FYI the current GM's with the 6.6 gas have their 6 speed transmission. In 2024 the 6.6 gas trucks will all come standard with the Allison 10 speed transmission which should handle the power much better and improve fuel mileage in the process.

I know 2 people who have the current 6.6 gas and both say it tows well but they both don't pull much over 10k. I would say if you're looking at a 11k TT (loaded) you'll be fine on the highway but it will slow down quite a bit and the heavy will hit some high RPM's on hills. Anything over that or if you battle a lot of hills the only option I know of in a gas would be the Ford 7.3 V8. With the 7.3 & the 4:30 rear axle ratio the F350 can tow well over 20k but will get 12ish daily driving and 14 max highway.
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Old 12-07-2022, 07:50 AM   #8
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FYI the current GM's with the 6.6 gas have their 6 speed transmission. In 2024 the 6.6 gas trucks will all come standard with the Allison 10 speed transmission which should handle the power much better and improve fuel mileage in the process.

I know 2 people who have the current 6.6 gas and both say it tows well but they both don't pull much over 10k. I would say if you're looking at a 11k TT (loaded) you'll be fine on the highway but it will slow down quite a bit and the heavy will hit some high RPM's on hills. Anything over that or if you battle a lot of hills the only option I know of in a gas would be the Ford 7.3 V8. With the 7.3 & the 4:30 rear axle ratio the F350 can tow well over 20k but will get 12ish daily driving and 14 max highway.

10 speeds are great, but they donít really seem to do much for mpg in what Iíve seen. The GM diesels, as you probably know went to the 10 speeds in 2020. The people with the 10 speed donít seem to get any better mileage than those of us with the prior 6 spd and same engine. I do see that people really like the 10 spd as far as how it drives. Always being in the right gear.

With the gas, Iíd imagine itíll be about the same. I agree the Ford probably has the best option for a gas engine and towing. The fact that engine is used in motor homes without too many complaints in power department would lead me in that direction. Plus, the GM gas engine HD trucks are still quite expensive, but at least one could avoid potential diesel issues.

With all that, over 10K lbs and towing anywhere with hills, Iíd go with the diesel if the your wallet has a stomach for that. Crazy what they cost though now at MSRP. I could buy a nice used 911 for what these new trucks cost. Wife would be a little more than p@&$&d if I sold everything for a two seat Porsche.
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Old 12-07-2022, 07:59 AM   #9
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10 speeds are great, but they donít really seem to do much for mpg in what Iíve seen.
You might be right with the GM. I know in 2019 when Ram went from the 6 speed to the 8 speed in their 3/4 ton gas engines the fuel mileage did increase as reported by many on the Ram forum. The reports I mentioned are not huge increases in fuel mileage my main point was the 10 speed will tow a little better than the 6 speed.
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Old 12-07-2022, 09:59 AM   #10
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FWIW, No experince with a 6.6, but I towed a 8.5k 5er with a 6.2 gas. Didn't give it much mercy. Did OK if you don't mind listening to 5k engine rpms when doing upgrades and in mountains or pushing strong headwinds. MPG was around 7, maybe 9 on a tailwind day on the interstate. Also had high engine temps when that truck got 80k miles the last time into the mountains. I think I wore it out. Own a Duramax now pulling 12k. Such a better overall towing experience, and I'm hoping for much longer service life from it. I know the OP was asking about the 6.6 gas, but IMHO, If a lot of towing is planned I'd skip a gas engine and go with a diesel if possible.
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Old 01-02-2023, 10:42 PM   #11
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I have a 2020, 2500hd with the 400ci gas engine. I pull a 2020 24RBS with it. Maybe 6,500-6,800 pounds. Sometimes throw in a 750 pound golf cart too. I have 18 inch wheels. It pulls good, gets about 10 mpg ont the highway, when towing, I have got as much as 19 mpg not towing on a freeway trip. Out on the interstate, it ďlikesĒ 65-66 mph in 5 th gear with the cruise set and in tow haul mode. Drop down to 55-60, it likes 4th gear better, not in tow haul mode. At 55-58 mph towing, there is no difference in gas mileage between 4th and 5th gear, according to my scanner, but it runs cooler in 4th. I would imagine that guys with 20 inch wheels and taller tires would do better in 4th gear on the interstate. Jay
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Old 01-15-2023, 02:56 PM   #12
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I had a 2020 Chevy with the 6.6 gas. I put 61,000 miles on it before I sold it. I towed our enclosed trailer, flatbed with track skid loader, our dump trailer and my camper with the boat behind it. The truck really performed well for a gas truck. Mileage empty was 15-16 and towing my camper and boat together was about 5. I had no complaints with the truck. I went back to a Duramax because some of my loads were maxing out the gas truck. I would not be afraid to get one with the 10 speed. That sure sounds like a winning combination.
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Old 01-16-2023, 10:13 AM   #13
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I tow a a 12k fiver with a 20' 2500hd ccsb. Pulls fine I get between 7.5 and 9.2 mpg depending on speed terrain and wind. Best road trip unladen has been 17.5 mpg. The 24' with 10 speed will no doubt have a lower calculated 1st gear more splits up to a slightly taller final drive. I would expect it to get slighltly better unladen fuel economy. And maybe a little better loaded performance on long ascents in the mountains due to better/ more numerous gear splits at hwy speeds
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