beowulf77

I’m at 3000 miles and still getting 17-18 mpg. When did yours loosen up... if you remember? im thinking of taking it in but seems like they are going to have trouble finding an issue with no codes. But maybe they have some sort of diagnostic they can run. also it is the same hand calculating it

I'll check the 25/50/etc setting. I hand-calculated my last half tank at fillup and got 19.8. The trip computer calculation was 17.2. So that's odd. I'll keep watching it. Just 1k miles so I will go to 2k til I take it in just to give it some time to self-correct.

thank you I was starting to wonder if it was a diesel thing or duramax 3.0 thing or what. I am new to diesels. Love it so far. I will revisit at 2k.

I posted a thread on it but I just got mine a cpl weeks ago... AT4 3.0L Sierra. Hard roll up cover installed. I can't seem to get over 17.5 mpg city or highway driving. I dont hard accelerate or brake... and am not sure if something is wrong or if it was my gas. I got it from QT up in Round Rock... not sure if that's relevant but QT in general has a good rep I thought. Not even sure what to look for to see if there's an issue. 420 miles. Was really expecting mileage in the 20s at least.

I have 420 miles on my new AT4 1500 Diesel 3.0L and the mpg has never been above 18mpg.... even driving home from the dealership on the highway for an hour. I've reset the trip computer and driven highway, city, whatever and it seems to stick around 17.5 mpg. I am not a heavy throttle guy at all and am very conservative on the gas and brake and all that. Is this a break-in thing? Or possibly a gas issue? I got the diesel from QT my first fillup. *EDIT* I am now reading their Cetane level is 40? I will go down this gas path a bit as it seems the most obvious. Any ideas? I bought this truck specifically for mpg in the 20s. Thank you