CMV157
Senior Member
Towing, my 6.7 seemed to get about 3 mpg better. Granted that was after $2k worth of deletes that definitely helped it. Haven't really determined empty yet. Driving 500 miles unloaded highway next week. Going to see and report my findings. *My 6.4 only had 4k miles on it so probably not entirely fair. I hear they loosen up well around 10k.