2024 Silverado 2500 HD with the 6.6 Gas (L8T) Engine

dbart · October 2, 2023

I am one of the ones that went from Diesel back to Gas...

First diesel was a 2004.5 Silverado with the LLY Duramax. Had no issues with that just wished at that time it had the 6spd Allison instead of the 5spd. 2018 I sold it and bought a new 2018 L5P Duramax SLT/Z71 CC. Had a ton of issues with it but it towed great and over the life of it at 84K miles averaged 16.7 mpg. Straight freeway driving was 18-20, to work and back was 16-19, around town about 14.

That truck got lemon lawed and when all said and done, I ordered a 2024 GMC 2500 AT4 with the 6.6 Gas. I was tired of the emissions crap, the cost of diesel, the fuel filters, DEF and just all the electronics required to run the new Diesels.

I have 5,000 miles on my new truck, and I love it. It tows just as well as my diesel, but I do miss one thing...the Exhaust brake.

I just did 965-mile round trip towing my Can Am in my 16' box trailer to Utah and back and I averaged 9 mpg, but my buddy's I was following all wanted to do 85-90 mph! UGH!

Had I stayed where I like to tow....65, I would have been in the 10's for sure. That trip in my Duramax probably would have been 12-13.

So far in the gasser, freeway driving can see 19 mpg, but it is usually around 17-18 at 65-70 mph.

To work and back 15-18, around town about 12-14.

I simplified my life going with the gas version, but I do miss the diesel just a little bit...only for knowing I could tow whatever I wanted pretty much. Now having said that, I won't ever get a trailer that is that heavy...so for me going gas just made sense and I love it.

~Dale

October 2, 2023

1 hour ago, dbart said:

I am one of the ones that went from Diesel back to Gas...

First diesel was a 2004.5 Silverado with the LLY Duramax. Had no issues with that just wished at that time it had the 6spd Allison instead of the 5spd. 2018 I sold it and bought a new 2018 L5P Duramax SLT/Z71 CC. Had a ton of issues with it but it towed great and over the life of it at 84K miles averaged 16.7 mpg. Straight freeway driving was 18-20, to work and back was 16-19, around town about 14.

That truck got lemon lawed and when all said and done, I ordered a 2024 GMC 2500 AT4 with the 6.6 Gas. I was tired of the emissions crap, the cost of diesel, the fuel filters, DEF and just all the electronics required to run the new Diesels.

I have 5,000 miles on my new truck, and I love it. It tows just as well as my diesel, but I do miss one thing...the Exhaust brake.

I just did 965-mile round trip towing my Can Am in my 16' box trailer to Utah and back and I averaged 9 mpg, but my buddy's I was following all wanted to do 85-90 mph! UGH!

Had I stayed where I like to tow....65, I would have been in the 10's for sure. That trip in my Duramax probably would have been 12-13.

So far in the gasser, freeway driving can see 19 mpg, but it is usually around 17-18 at 65-70 mph.

To work and back 15-18, around town about 12-14.

I simplified my life going with the gas version, but I do miss the diesel just a little bit...only for knowing I could tow whatever I wanted pretty much. Now having said that, I won't ever get a trailer that is that heavy...so for me going gas just made sense and I love it.

~Dale

Solid information and beautiful truck.

I had a 2015.5 Denali Duramax and mostly loved it. My recreational trailer is only 5500 LBs which is like not towing at all. I pulled some 10-12k stone trailers and it still hardly taxed that motor.

Moved into a different need with less payload required for work. Bought a 2020 6.2L 1/2 ton. Pulling the same rec trailer fully loaded with family, generator, paddleboards, etc, I have averaged over 10 MPG in 4 years of use. I can go up the Eisenhower at 75 MPG and any other pass if I really push it. Without a trailer, I average 18 in mixed driving, and when needed, it is plenty quick to 60. I have nothing but high praise for it, and if you can live with the 1360 LB payload, it is a jack of all trades.

My needs will change early next year and again require the capacity to put 2500 LBs in the box. So I am likely to go back to a heavy duty, but really have no need for the diesel. My 2015.5 had the normal sensor issues and DEF tank replacement, and thankfully all were fixed under warranty. The gasser with 10 speed should suit me fine. Of course I will miss the added grunt of the diesel, the sound of that motor, and as you mention, the exhaust brake. My 6.2L 1/2 ton uses engine braking surprisingly well, and I hope the 6.6L HD will be reasonable.

rjgvt · October 3, 2023

7 hours ago, dbart said:

I am one of the ones that went from Diesel back to Gas...

First diesel was a 2004.5 Silverado with the LLY Duramax. Had no issues with that just wished at that time it had the 6spd Allison instead of the 5spd. 2018 I sold it and bought a new 2018 L5P Duramax SLT/Z71 CC. Had a ton of issues with it but it towed great and over the life of it at 84K miles averaged 16.7 mpg. Straight freeway driving was 18-20, to work and back was 16-19, around town about 14.

That truck got lemon lawed and when all said and done, I ordered a 2024 GMC 2500 AT4 with the 6.6 Gas. I was tired of the emissions crap, the cost of diesel, the fuel filters, DEF and just all the electronics required to run the new Diesels.

I have 5,000 miles on my new truck, and I love it. It tows just as well as my diesel, but I do miss one thing...the Exhaust brake.

I just did 965-mile round trip towing my Can Am in my 16' box trailer to Utah and back and I averaged 9 mpg, but my buddy's I was following all wanted to do 85-90 mph! UGH!

Had I stayed where I like to tow....65, I would have been in the 10's for sure. That trip in my Duramax probably would have been 12-13.

So far in the gasser, freeway driving can see 19 mpg, but it is usually around 17-18 at 65-70 mph.

To work and back 15-18, around town about 12-14.

I simplified my life going with the gas version, but I do miss the diesel just a little bit...only for knowing I could tow whatever I wanted pretty much. Now having said that, I won't ever get a trailer that is that heavy...so for me going gas just made sense and I love it.

~Dale

Great write up and nice truck! I’d like to get a 24 AT HD in February or March. Currently have a 2018 GMC 1500 DC 6.5’ box but want an HD gasser, no cylinder deactivation or start/stop. Don’t need an HD but like them.

Going to call the dealer tomorrow to get an order started if my sales guy is in. Need to get through hunting season then will have time to get an ARE cap ordered and installed.

How do like the running boards? I’m on the fence between those or the wider ones that sit a couple of inches lower. Yours are definitely slick looking.

Handy · November 8, 2023

I received my 2024 2500HD 6.6 gas in July and just did my first oil change at 2290 today with zero oil consumption. I love this gas engine after having the Duramax in 3 trucks since 2001. The 10-speed trans is amazing and I love it also. I just drove 600 miles last weekend, freeway miles, and averaged 15 mpg. I towed a 10,000 pound trailer about a month ago for about 160 mountain and desert miles and got 7 mpg.

John Mc1975 · December 19, 2023

I have a 2020 2500HD 6.6 gas with 78000 miles. The truck does consume a few quarts between changes. I just added 3 qts with about 22% oil life. Also make sure techs are completely tightening the filter, it is in a tight spot and I had loose filters twice in the last 3 yrs.

9thShodan · December 25, 2023

I had a 22 3500 Denali dually gas and put 41000 miles on it. Changed the oil every 5k and it was always on the money. Never burned a drop. I traded that in in March for the 24 Denali 3500 dually gas and just did the 3rd oil change and didn't burn a drop. It's always right on the line. Great truck, I hear people complain about things but I've never had an issue and I tow over 20k up the mountains in VA regularly.

lschafroth · May 19, 2025

I have a 2020 GMC Sierra 2500HD AT4 6.6 L8T gas and it uses zero oil between changes. Have 83K on it.

Chuck FB · May 22, 2025

On 5/19/2025 at 4:01 PM, lschafroth said:

I have a 2020 GMC Sierra 2500HD AT4 6.6 L8T gas and it uses zero oil between changes. Have 83K on it.

Has there been a particular oil brand or type within that, that you've been using for your truck since you've owned the truck ?. Also what typical miles as well as oil life percentage do then change the oil at ?

lineman1234 · May 22, 2025

6 hours ago, Chuck FB said:

Has there been a particular oil brand or type within that, that you've been using for your truck since you've owned the truck ?. Also what typical miles as well as oil life percentage do then change the oil at ?

Why would that matter?

I buy at walmart, sometimes local napa, what im in the mood for as long as it is the correct oil, i dont buy the same thing in a row, or if i do, its by accident. I use a reusable oil filter.

Mine doesnt use any notable oil between changes. And, i change when its convenient. If traveling i will do it early at times and if needing to get back to where i can change it its the recommended numbers or close to it.

Right around 33,000 miles.

Chuck FB · May 22, 2025

10 minutes ago, lineman1234 said:

Why would that matter?

I buy at walmart, sometimes local napa, what im in the mood for as long as it is the correct oil, i dont buy the same thing in a row, or if i do, its by accident. I use a reusable oil filter.

Mine doesnt use any notable oil between changes. And, i change when its convenient. If traveling i will do it early at times and if needing to get back to where i can change it its the recommended numbers or close to it.

Right around 33,000 miles.

That's a good question as to why would it matter. The fact is although all the oils if lets say for this engine that are chosen and meet the spec of the Dexos 1 Gen 3, that doesn't mean they are all formulated exactly the same as some have an additive package that is in theory designed to last longer before the additives are used up than another oil blended by the same manufacturer. Having said that if the engine has its oil changed more often for its given use so that none of the oils taken off the shelf have been run past their useful life, it matters far less what oil flavour was chosen.

I wanted to pick this gentleman's brain because of the vintage of his truck as that is where the beginnings of the whole "my L8T uses oil" theme began with that engine platform and the miles he has accumulated which is more than what some on here have accumulated so far on their trucks. GM pushing harder for longer oil change intervals just like all the other manufacturers .... but not all truck owners abide by that as some go even further, while some are old school like myself and have kept with shorter drain intervals that used to be the standard practice years back. I have so little data on my own truck due to the limited miles so far as that will take some years to see how my own engines future plays out. Whatever oil type and distance between changes that Lannie is doing, his engine seems happy with that.