i traded my 07 5.9 for a 12 6.7. Yep, the mileage does suck. if you get 15 stock you are doing the grandpa and lucky at that. However, the truck (DRW 4WD) is a towing beast and the Engine Brake is actually a good functioning addition. I am considering deletes and a tuner before they are all gone to improve the mileage. If I could get 18 I would be VERY happy. I would not, however, trade back.