Ok , I did a nice compilation of 2 different mpg over a month period and the results are always the same(by hand) . Same highway, same distance, and+or- same weather. And the trucking rule I`ve learn over time looks like to be the same with the 6.7. First, 1950rpm(+-65mph) gives me 18.7 to 19.2 mpg and secondo, 2200rpm(+-72mph) is 14.7 to 16.2mpg. Results are always the same over a month. The 18 wheeler rule we use is from 55mph every 5mph faster is 10% more fuel+-. The test is done on a 07 6.7 manual quad 4X4 long bed. So.....slow down I guess :sly: Sorry I always use rpm as a reference....trucker`s way to do it!