Seems like you have always reported pretty poor fuel mileage on your trucks you had a dodge before this truck, a 5.9 if I'm not mistaken and had the same gripe. I think you have some oddity in how you use it that you don't say or don't think of. We pulled a 17k+ pound dozer/trailer combo with an '05 duramax and got better mileage than your getting and I'm betting whatever you were towing was 1/2 that.

What size tires are you running?

I would be the last person talking about MPG, driving a Toyota. That said, my last ride was an 08 Dodge 3/4 Ton mega-Cab, 4wd with the 6.7 Cummins. Loved the truck, but after 176K, it still didn�t pay for itself. MPG was about 3 more than my Yota gets, Fuel, generally $.25 a gallon more than gas. Way more maintenance costs that a gas burner. I loved the diesel though. Towing was outstanding. It was 3 years of AC problems that no one was able to fix that drove me out of the dodge and into the most reliable pickup on the road, the Toyota Tundra.