[38Chevy454]

I have twin screw rear and 45 ft length and approx 36K lbs for the coach. Cummins ISX15 and 10 speed Eaton Ultrashift. I typically run 70-72 on interstates, which is about 1550 rpm for me. I think I have 3.36 rear gear, but have not ever really checked for sure. I don't regularly check mileage, but it is around 7 mpg. Mine is not aerodynamic, so I might do better if I drove slower. Usually towing a toad around 4K lbs, sometimes a trailer with car on it around 6K lbs. Toad or trailer does not make much difference in mpg, but can feel it when accelerating from a stop.

My engine has EGR, but no DPF or DEF. I have heard of 10-15% increase in mpg with an EGR delete, but nobody seems to have the real programming figured out to avoid the CEL and getting max performance potential.