Back before I had to park my 87 with the 6.2 because of frame rust I hauled my Ford 5000 diesel to Illinois with it from Nebraska. A little over 400 miles up and down lots of the Missouri hills on Hwy 136.
RPM was never a worry as long as I maintained legal speed coming down the hills. Going up the hills I would put her to the floor and let her bark thru the glasspack dual exhaust.
Wish that truck wasn't rusted out. It made up in MPH what it lacked in power. DOUG