If this helps, I have an 2004 F350 6.0 diesel 4:10 rears and pull a 12,000# trailer (20,000# gross) as in signature. I set cruise at 60 mph (just under 2,000 rpm) put in Tow/Haul and it went up and down hills of PA I-80, I-81 thru Scranton and I-84 to CT and did not miss a beat. It would drop a gear rpms between 2,500 and 3,000 depending upon hill. Engine and trans temp just sat there like not an issue. On the 90 degree days the engine fan would cycle once or twice on a long hill. 18 mpg just running around. Towing 10-12 mpg depending upon terrain.
I'm sure the newer ones would do much better.
