I bought a new 2007 Dodge Ram 2500 with a 6.7 with the 6 speed auto, 4x4 & 3.73 rear axle in Sept 07.
I have recorded every drop of fuel since new and today it just turned over to 25,000 miles. I planned to get this truck for over 6 years and for a truck of it's size it is fun to drive with more power than I ever expected. Overall it is a very well behaved truck and very smooth compared to earlier trucks.
The aftertreatment system is the worst part of the truck. Dodge has replaced the complete system once - all parts including the DPF, Nox filter, turbo, complete EGR system and sensors in the system. Best mileage ever on a long highway trip running 60-65 was 19.3 mpg - the 5.9 models have done 23-24 mpg on the highway. Average mileage since new is 16 mpg with some days 17-17.5 mpg. During regen, the mileage drops to around 15 mpg, when not regenning it gets 22-23. The regen is the problem. Mine is 100% stock with no aftermarket mods, but some have installed removal kits and their economy jumps immediately by anywhere from 3-8 mpg.
Looking back, I should have got the 5.9 engine as it was a transition year in 07 and those built in 06 were all 5.9 engines. Although I like driving the truck, the constant updates and fixes have soured me on keeping it and I'm probably going to go back in time for a pre-07 emissions diesel. A Jetta TDI fits the bill for a commuter but I also have the need for hauling so not clear how this will turn out.