Most diesel engines are designed to run on the governor, all day, every day. What is the "red line" on the 6.7? I've not driven one, but I know my 6.0 is 4000+ for the red line. Running 3000 and under shouldn't hurt anything, except fuel economy. 2500 at 70 isn't too bad, as my 6.0 runs 2000@70.