Doodle

I think this 10 speed is the best transmission I’ve ever had in any vehicle. I have a 15 LML with the 6 speed Allison and it’s fantastic too, but this 10 speed is more refined IMO. Only thing it does sometimes is downshift kind of harshly when coming to a stop. Not all the time, just occasionally. Like it gets confused which gear to drop too. Guess time will tell on reliability but if they put this transmission behind the diesel I can’t imagine any situation where you could hurt this with a gas engine. Just keep an eye on the temps and should last a long time.

The 6 speed is a great transmission as well. I think the 10 speed keeps the 6.6 in the power band a bit better but I had no issues with the 6 speed in my 23. Main reason I traded my 23 for a 24 was I got an AT4 and my 23 was an SLE. I like the looks of the SLE but I hate the fact you can’t get a console and leather seats with the SLE. With the Chevy you can upgrade an LT with those options. I guess as I get older I just want to be more comfortable. Plus I have three kids and there was two cup holders in the whole pickup. Didn’t even have the rear seat flip down. I honestly think the 6.6 gas will end up being a very reliable engine. I’ve honestly never heard of anyone having any issues with them other than some oil consumption. They have been out 4 years now so there are some with over 100K for sure somewhere. My only complaint is the fuel mileage. I wished it was better but these things also weigh a lot and sit way up in the air. So far the 10 speed is no better than my 6 speed. I was hoping it would be a bit better. It does seem to do better with non ethanol gas. Most of the time I never see any significant difference with my 5.3’s on E10/15 compared to regular but for some reason this 24 seems more sensitive. Problem is E19 vs regular 87 around here is about $0,60-0.70/gal cheaper so it doesn’t really make economic sense to run regular.

I think the 6.6 gas is going to be just as reliable as the 6.0 gas in time. I have had a 23 with the 6 speed and now a 24 with the 10 speed. I will say the 24 will pull as much as my 2015 Duramax, it will just get terrible mileage (6-7 mpg). I pulled this trailer the other day and I was grossing 30K total combined. I should have never loaded this heavy but only had to go 25 miles. Pulled the load at 65 no issues other than watching the gas gauge drop. My lifetime mileage with 10K on the 24 is about 12.5. My Duramax has a lifetime of about 14.5 with 130K on it. However it’s actually cheaper to run the gas with the current fuel prices. I’ve never had any oil consumption issues. Only complaints I really have with my 24 AT4 is it has lots of little dash and interior rattles. Might just be because of the stiffer suspension but it’s kind of disheartening with what we pay for these things. I would not buy a new diesel again unless I was towing all the time. That’s where diesel shines. I tow seasonally, but heavy. The 6.6 will get the job done but it’s definitely not a diesel as far as torque goes. I would have to think these new 6.6 gas should easily hit 150K with minimal issues at all. The new 10 speed is butter smooth and a big improvement over the 6 speed in my opinion but the 6 speed was good too.

Had a 23 put 15K on now have a 24 with 10K. Mileage is about the same. My 23 was an SLE and weighed about 7150 lbs. My 24 is an AT4 and weights a tad over 7500 lbs plus it has the 20” tires. So given that I’m glad it’s about the same as the 6 speed. I would not pull the trigger just for mileage. The 10 speed is just a more refined trans and is just makes the power so much more useable. The more miles I put on the better I like it. Butter smooth shifts too. My 23 took to about 10K to get broke in so the mileage could go up a tick, but I”m guessing very minimal.

Yeah there are so many factors when it comes to mileage. Every blacktop road around here is minimum 65 mph. We are flat and wide open in western KS. Nothing like Vermont. If I drove 55 here I'd feel like a snail! I also live at 3500' elevation so that makes a difference too, but the flat geography does help mileage. Where I live there are essentially no hills and what we might call a hill people back east would laugh at. No such thing as "steep grades" here. Ha ha.

To be fair I don't think my LML would do much better than 17-18 at 80 mph. In my area diesel is approaching $1.50/gal more that gas. So it's still cheaper to drive the 6.6 gas than the diesel right now. Kind of glad I have both. Just let the LML sit unless I need to tow heavy.

Another update on mileage. I took my 24 on a 600 mile roadtrip all highway this past week. I was fighting a little wind from time to time (I live in Kansas) but I was traveling between 69-80 depending upon if I was on the interstate or state highways. I noticed once you get above 70 mph mileage really starts to drop. At 80 I was getting about 14-14.5 roughly. At 65-70 closer to 16-17. Think my average tank was about 15 or so on that trip. Kind of disappointed in the mileage at interstate speeds as it’s holding 10th gear fine, but also realize these things sit way in the air and are heavy. On one flat stretch I put it on 60 mph cruise just to see the difference and it was closer to 18-19. Only 7K on it so far. My 23 started to get a little better around 10K so guess we’ll see. Also the first tank of fuel I ran was 89 octane. Just wanted to see if there was a difference. I guess I’d say there was no noticeable difference.

I have had the same experience. Have a 2015 diesel, had a 23 6.6 gas, and now a 24 6.6 gas. Towing 6000 lbs is nothing for the gas. I live in western KS where it is flat, but I have no issues pulling 12-14K with the gas. Once you start getting up to 16-18K a diesel will be better. The 6.6 gas can do it, but it will rev a lot and gas mileage will be 6-7 at best. My 24 gas actually has a higher GCVWR than my 15 diesel. That is primarily due to the frame and brakes, but the diesel will definately pull heavy loads much easier, but it does show the gas is more than capable. I can speak to experience on the 6 vs 10 speed. They are both great transmissions. The 6 speed was more than capable. They 10 speed just keeps the 6.6 in a better powerband when towing. I actually thing the 6 speed was quicker unloaded than the 10 speed but towing wise the 10 speed is better in my opinion. The 6.6 gas has been out since 2020. So far they have proven to be very reliable, much like the 6.0 gas. Not saying the L5P isn't reliable, but if you do have issues it's gonna take big dollars out of warranty plus the $10K upfront cost. Mileage wise I get 12.7 with the gas and my 15 LML I'm 14.5-14.7 average. With our local fuel prices that's a wash plus I don't have to use DEF or additives with the gas. If I towed heavy all the time I would get the diesel as the economics would work out better for fuel mileage. I might tow 5K a year. Not worth it for me to have two diesels. The newer diesels are monsters for power. If you like or need that you will not like the 6.6 gas. If you just need something reliable with cheaper upfront cost that will still get the job done I'd go for the 6.6 gas. I have said many times I wish GM would come out with like a 7.0 with 450 hp/500tq and that would start to close the gap a bit between gas and diesel. Maybe with some tuning that's already attainable with the 6.6.

My 24 is very accurate as well, Best computed average I’ve ever gotten with a GM product. I’m at 5000 miles now and was hoping unladen mileage would come up. Best I can get pure highway is maybe 16.5-17. My lifetime average is 12.7 so that’s not bad with a mix I guess. My 15 LML only gets about 14.5 average so with the cost of fuel it’s a wash. My 24 gas AT4 CCSB weights almost 7600 lbs empty. My LML SLT CCSB weighs 7850. These new pickups weigh quite a bit more and they sit up so high in the air, mileage is just gonna suffer some. For reference, I had a 2008 LMM CCSB that only weighed 7200.

Great comments and feedback. I have not towed with my 24 much yet, but I actually do like the transmission compared to the 23 6 speed I traded in. In my opinion the two transmissions are totally opposite. The Allison gets a heavy load moving easier, but seems to get real busy once up to cruising speed. The 6 speed was doggy to me getting started but would hold power better once up to speed IMO. With the 6 speed i generally never saw it shift much out of fifth with a load, the 10 speed will shift all the time and I really don’t know what gear it’s in. But the Allison does perform well, it’s just a different driving experience. The Allison is butter smooth so if you aren’t paying attention to the rpm’s you really don’t know it’s shifting much. I would not fear pulling up to 26K in my area with the gas, its just mileage is gonna be 6-7. I still have a 2015 LML so most of the time under heavy tows I’ll just use it but the 6.6 gas can do it. I do feel like GM left some on the table with this engine. I know whipple came out with a new supercharger, but it’s like $7500 so that make no sense, might as well get the diesel.

I have not experienced this with my 24 but you can definitely hear a little more “noise” with this transmission compared to the 6 speed I had. Not annoying or anything but it’s there if you listen. My feeling though it because the pickups are so quiet now. Hardly hear the engine.

The computer actually read 15.1. The 15.2 was hand calculated. I’ve never had a GM read low. Always at least a half mile or more optimistic.

Just got back from a 900 mile roundtrip (unloaded) with the new GMC. Running anywhere from 69-80 depending upon which highway I was running on. Averaged about 15.2 mpg which I was pretty happy with overall. Still at less than 2500 miles so might get better in time. I think if I ran 65 this thing would get 17-18 pretty easy. Amazing for a pickup that weighs in at about 7500 lbs and is way in the air with 20" wheels. I was really impressed with how well the transmission keeps the 6.6 in the powerband. It cruises effortlessly on the interstate and I can pass with ease with just a blip of the throttle. The 6 speed had no issues either, but you can tell this transmission is just more refined and in tune with what the engine is doing. The more I drive this thing the more impressed I am with it. I think if GM ever came out with something like a 7.0L gas with 450-475 hp and 500 tq with this 10 speed, there really wouldn't be a big reason to get a diesel unless you were towing heavy all the time. The 6.6 gas is great but I just think they would grab a big chunk of market share if they had something with just a touch more power. But then I'd probably just say "I wish they made 500 hp" so it probably wouldn't matter, lol.

I wouldn’t worry much about 7.3 gas. Internet causes people a lot of grief Most of the time shouldn’t worry about. I have a 2015 LML with 130K and people act like they are all destined to blow fuel pumps. I know it happens but it’s a small percentage just like lifter failures on 7.3’s. If it happens to you then yeah it sucks, but the chance is likely small. Having said that, I’m happy with my 24 gas and it is a great platform. My 23 didn’t use any oil and I don’t have enough miles on the 24 to report if it uses oil yet.

I once put a Blackbear tune on my 2005 6.0 gas. It woke it up significantly. That was with a 300 hp 4 speed!