Loosing speed going uphill and revs at 3500 rpm+

Ok. A 29’ class C should perform very good with the V-10. My 02 has a combined weight of 18000lbs and I can maintain 60+mph up a decent grade.
And yes 4K rpm from a V-10 Triton is ok, that’s where it’s making its power.

You had a truck hooked up to your class C? I’d that how I read your last post? If so that is asking a lot of the V-10!