It takes a while for a Duramax to get broke in, But yeah I wouldn't expect to much. I've seen lots of posts with people averaging 11-15mpg. Little surprised the best you have seen on the highway is 14 though. That seems a little low unless you were running 80 or something. A diesel HD only really saves money on fuel if you tow with it a lot. My average on my gasser after 5800 miles is 11.8mpg. That's mixed driving with some towing. I would think the diesel would be closer to 15mpg average. Still not really saving anything at 15-16mpg though. Not when you factor in diesel vs regular. Plus DEF, fuel filters, ect. Diesels just cost more all around really. No free lunch lol, Got to pay for that 910ft of torque!!
6.6 or 3.0? Huge difference.
Im assuming this is a hd? If so my milage started jumping up around 1200 miles into it.
I think that's how these motors break in. I couldn't break 12 mpg until after 1500 miles, now at 2200 miles I can get 16+ around town, which is good. Haven't done a road trip yet. Most of my highway work was towing in hills and was only getting 11-12 mpg. Your's will get better.
This is 9000 lbs of big ass truck rolling down the road sitting 7 feet in the air and 7 feet across. It's basically like trying to push a barn door through water. There's no aero on these pigs. It's a miracle you can break 10 mpg.
Yep, just like mine!
Yeah, my bad, I didn't see a signature and made a bad assumption.
I'm right there with you! I have been very disappointed. I have a brand new in the box 56 gallon Titan fuel tank ready to be installed! Since I'm only getting 12-13.5 no matter how I drive I have been dreading pulling my boat long distances!this is my 4th Dmax and I never saw this low mileage unloaded! My 3500 LML Dually was consistently 16-18 with a lea foot and would drop to 8-10 towing my 12k pound boat! I'm sitting at 2200 miles and it's not changing! I can't wait to see what it gets during regens! Does anyone remember how many miles they had on the first regen? I can't wait till programming is out and she can go on a weight loss program!
From my understanding they regen atleast once every 800 miles. 4-600 miles is average. But at 800 it will regen regardless. It's like a built in timer incase the various sensors fail.
Lol, no worries. I figured when you had a 450mile average of 25mpg. I know lots of people with 2500s. Ain't none of them averaging 25mpg. My brother n Law bought a Comaro for a commuter car to save on fuel compared to his lifted AT4 2500 lol. I had a tuned LML and the best it would do was 22. But my average was around 15 with mixed driving. These new ones are 7' tall and are pushing 9k Lbs. Not to mention stock 35s. Sitting by a half ton ZR2. The the 1500s look small. Which is funny because the same 1500 made my 2011 durmax look small.
Fuel mileage my ass, tow that Jeep around with your HD and you'll improve your mileage across your fleet.....LOL.
. Maybe 2 motors for twice the fun. I found a image, nice console boat
. He's not really worried about fuel consumption. 
