I allow my LBZ to get good mileage.
We all have discussed this many times, but I'm convinced driving style is the major reason some do and some don't get good mileage with the Duramax or with any vehicle for that matter. I have friends that don't get good mileage and others that do. I am not an aggressive driver and I always use the tow-haul for grade braking. I coast into a red light or stop sign rather than drive up to them at full speed and slam on the brakes, etc. I don't act like I'm on a drag strip when leaving the stop either. I get 20 mpg more or less with my 2006 LBZ when driving 65-70 mph. If I speed up to 75-78 I get 19 or slightly less. I live in Georgia so most of my driving is relatively flat. These numbers are hand calculated because my DIC is always a little lower. No problems with mileage for me. I would suggest that those that don't get good mileage can't help but enjoy the tremendous performance capability of these trucks a little too frequently. It is tempting as we all know.
Ed