R_D: Be patient. The mileage on my '08 2500 Maxi Cummins didn't start to get good until after I hit 10K. I didn't mind. The tighter tolerances of the engine will help it last longer. Mileage has steadily increased with the miles on the truck and now, at 20K, I'm getting 12+MPG pulling my mini excavator (about 15k #'s) around town to jobs, and just this week got nearly 22 MPG on a 6 hour trip with about 3/4's of a ton on the truck. Get some miles on the truck, leave the programming alone (Daimler did a great job of applying the Bluetec diesel technology to the Cummins), and the Allison 6 speed works flawlessly to match engine speed and load. Mileage that far exceeds any hint of an EPA rating is coming your way. I absolutely love this truck. I've had many trucks in my 40+ years of construction - this is the quietest, best riding and handling, most fuel efficient one I've ever had. The family votes to take the Maxi on all family trips, and I don't mind 'cause I love driving it. The stereo kicks A$$ too.
By the way, to answer another question: My dealership, Greenbrier Dodge, offers synthetic oil changes for the Cummins. Unfortunately, I can't afford to have them do it for me, but I use a major brand that has both Cummins and Dodge approval for warranty coverage. It may help with my incredible fuel mileage, but I can't verify that. I've been using it since my first oil & filter change at 4K, so I don't have a before and after difference to compare, and that comparison would be flawed because of the low mileage on the truck. Maybe at 30K I'll try a load of conventional oil and compare and repost, buuuut, maybe not! I like things the way they are.