I am a retired trucker. When I was in the business, I met a driver that worked for a small Caterpillar test fleet out of central Illinois, who showed me fuel mileage records that were astounding. He was running a 550 horse Cat, 10 speed tranny, and usually above 70,000 lbs gross weight. He never got in a hurry, never used his cruise control, and kept his top speed at 55 mph unless on a downgrade. His statement to me was that "you wouldn't want run with me."
We will be leaving for a trip from PA into numerous favorite places in Colorado in August . It will be a lengthy trip and my first time behind the wheel of a diesel motorhome. I traveled the same routes in our 460 Ford powered 34 footer and the fuel mileage was terrible. I was not retired and therefore always in a hurry.
I do know that good advice is to keep your speed down, keep your cruise control off, keep your RPMs down, stay off the accelerator on a slight rise in terrain. Let your speed drop on those slight grades. The amount of time that you lose at the end of the day will really not amount to much, and probably save a lot.