Here is a quick highway drive of a 2017 Ford E-450 DRW 6.8L 2-valve V10 Triton, a 15ft truck from Uhaul. Normally I would't subject myself to Uhual but they are the only ones who had a car carrier capable of carrying the weight of my truck. My average mpg was 7.3 over 700 miles and the total combined weight of truck/load/trailer was roughly 17,500 lbs. Keeping the truck at about 75mph the RPMs constantly floated between 2,600 and 4,800. But mostly ran full throttle at the latter. Watch closely at the gauges you will notice how little if any it accelerates at full throttle. The absolute worst things about this truck is no cruise control and how crazy loud the cab is.
