Mike
The sweet spot for the Durmax is about 1800 rpm. At that range you should see a increase in mpg. Our trucks still are not broke in yet so after about 10 to 15,000 miles you should see an increase. Try running about 70-72 mph and see if doesn't increase. I will be putting my special oil in here shorty. It is the same oil we had blended up for all our road tractors and it increase our mpg by 1-2 . It lower the fiction, when you lower the fiction you lower the heat in the motor also. We also ran this oil in our thermo kings refers.
Steve

Good deal. Yeah I know lower speed will increase efficiency but 80 just feels like it covers ground a lot faster. Lol. My 2500 gas truck would get 16 at 65 and 13 at 80. I still ran 80. Lol. Quite happy with the mileage so far for what the truck is.

Steve ill talk to ya about that oil when your back down.

That's a beauty! Best of luck.

I get 21 - 22 between 65 -70 mph on my 2015 Durmax. Have 1500 miles on it so far. Pulling my Topgun only 10 mpg. Love this truck better than any new truck I've bought new since 1986.

Me too

That's one sweet ride. I haven't out grown my 08 yet but damn those new ones are nice.

Just a little update. Just did a run to Miami. 325 miles round trip from Cape Coral. Truck did awesome and the comfort is unbelievable. So far it has proven to hover around 16 mpg at 80. Unless in regen, caught it on this trip. 30-40 miles of 11-12. Once warranty is gone so is dpf, def, and egr. Lol