I have a 2001 duramax 2500 hd with allison auto trans . 120000 miles I had the dealership change out the injectors since then my milage best has been 16 . before this I was getting 19 to 21 . what do You think the problem is.

Yep I am seeing the same thing, I did get 18 the last tank but it was 100% highway with a good tail wind. My towing milage went down also.
It runs good and pulls good but the milage thing.

Same thing here as well. I got 19-21 before the swap, now I'm lucky to 15-17!











Of course I've gained weight in my right foot so, from time to time it's my fault!):h

mine always starts gettin crappy when the fuel filter gets dirty.... plus i use the skinny pedal very "liberally" so that dont help....

You will know when your injectors are shot, when the truck billows blue smoke at idle and high speed, and your tailgate turns black with soot.

You will know when your injectors are shot, when the truck billows blue smoke at idle and high speed, and your tailgate turns black with soot.
What does this have to do with mileage?

I think it will pick back up again. It seems the injectors have to go through a "break in" period. When I bought my truck, it had brand new injectors in it with 0 miles on them. I was getting the same MPG as you. Now after 18,000 miles, my mileage is 20-22 consistantly.

Just my .02:cool:

MPG?????? Don't know, don't drive the HD anymore, FUEL too HIGH!!! :mad:

The absolute best I have ever seen was nearly 18. Usually between 15-16.5 More so on the lower end, with it dipping in to the 14's sometimes, down into the 13's when pulling a 10,000lb skid/trailer combo.

after injectors were replaced at 157k miles, mileage went south too and now at over 193k miles mileage is picking back up. I am stillnot at the 24 mpg but I also think ULSD is the problem...22 mpg is the best I can do now

I don't know if this may help you, but I just got at least 1.5-2 mpg after changing my fuel filter.

My 02 , bone stock, and light footed gets 17.5-18 mpg at best. 105k miles, original injectors. With my sled deck and two sleds .... 9 mpg, not very happy with the mpg, but sure do like the Chevy. I drive a 04 cummins , company truck, 15 mpg, fully loaded and alot of idle time. Dino

x2

I was getting 22 mpg out of my 02, but ever since the mandatory Ultra Low sulfer fuel was put out, I lost 4-5 mpg. Even with the Biodiesel I still get lower mileage, obviously since it is 80% diesel and 20% bio.