I agree with hipower that years ago they didn't have these monster engines that a lot of people want on a RV that weighs any where from 26K to 45K. Some of those big rigs have the same Cat or Cummins engines that are on motorhomes but pulling a lot more weight. I think that most of this complaining about not enough power is not so much the engine. I really believe it is the person inside that coach that does not know how to use the gears properly.
I have a 3126-E Cat engine on my coach which with toad and all is probably pulling around 34K pounds. I just got back from a trip which took me through Donner Pass, and all the way up to 10K elevation near Mammoth with no problem at all.
I agree you can not go up at sixty miles per hour, but it will climb steady at 45 mph by shifting gears down and keep watching that tach.