[porky69]

My Haulmark has a Detroit 515HP/1650FT-LB with a 12speed Freedomline Autoshift and it has more than enough power for any hill I have ever encountered on public roads, very rarely falling more than 5mph under the posted speed(the mountains in British Columbia are similar to what you mention) Also more power requires more cooling capacity, which most chassis are limited on, on a long (3+mile hill)the engine fan is screaming to keep it cool. Most highway haulers (80,000lb or more) run lower power levels than this so 1850 or 2050 ratings in a RV are pretty much showing off. Acceleration with the autoshift is on par with the Allison but the exhaust brake is more effective with the autoshift (more gears keeps the rpms closer to optimal performance range)

I can't speak for the Eaton autoshifts but mine skip shifts if it senses the conditions are right, but has the extra gears if you need them.

I have long hauled and heavy hauled with trucks ranging from 300hp to 600hp with Allison 5&6sp, Fuller 9,10,13,15 and 18sp (some with 3 or 4 speed auxiliaries), both autoshift and manual.

If I were to build one from scratch I would go in the 500-550hp/1650ft-lb range with a 13 or 18speed (manual for me personally, but understand why one would want an auto). More than enough power for a 45,000lb RV setup.