My 6.2 F350 in carry the camper mode runs same rpm as OP said. If head or cross wind has it shift from 6 to 5 a lot I select to limit top gear to 5. It sometimes choose gear 4 and runs along at 2500 rpm for miles. It never sounds like it is “lugging” or frantic, seldom revving above 3500rpm unless you apply lotsa throttle. This is on 87 E10 gas.
This would be a super fun engine if it had “EcoBoost” stuff.
The cruise control allows more mph drop before downshift than I like. I can get it to hold speed and not shift in manual throttle mode.
I’m going to try some 91 gas once I get road tripping. A friend tows with a 5.4 Ford and the engine management likes 91.