Hi,
My motorhome has a 96 F-53 chassis with a 460" engine - 7.5L and factory rated at 225 HP at 3,600 RPM. Due to the nearly 1 liter per cylinder, the engine will not rev up as high as the smaller displacement 4.6L V8 with less than .6 liters per cylinder. So running at 4,000 RPM all day long is fine with your engine. Up a small mountain, it is fine too. . .
I think you will be fine on the mountains, just take it easy. I drove from Ill to Yellowstone in my motorhome, towing a car twice.. It went well both times. Up the hills are only 45 MPH in second gear, and then going down the hills, I always lock out overdrive at the top of the hill, before picking up much speed. Then if I felt uncomfortable, and the RV is picking up to much speed, I could slow to 45 MPH, then shift to 2 gear (of 4 speeds).
Fred.
