I have since 1989, been saying; If you can get that kind of mileage, bring your pickup and I'll let you hook on my Arctic Fox. I will bet you all the fuel you want to burn you can't get over 10MPG from N Va to Ohio and back via RT 7, 522, I 68 and I 70 then down I 77, I68 to I 81 and back here. No one has ever taken me up. I have driven 3 diesel pickups into the ground and you need to go get the HP developed/lb of fuel burned formula and find out what you do burn in your 300 hp Cummins.
http://performancedevelopments.com/fuel-flow-calculations-for-horsepower/