My comments above were based on our personal RV'ing experience in our Ford chassis motorhome.
In our fully loaded 24 foot Class C based on the E450 Ford cutaway van chassis (with 4:56 rear differential gearing, as opposed to the E350's 4:10 differential gearing) we can easily travel up long highway 6-8% grades at 55-60 MPH speeds - about the same speeds as the diesel motorhomes traveling on the same highway at the same time. We have even done this at sustained altitudes above 8000 ft (High Sierras and Eastern Wyoming) ... but we have to rev up our V10 to do it. Our doghouse insulation is pretty good, so the ten cyclinder whirring sound is not irritating. We don't always drive this way, but can if we want to.
The reason I mention all this is to inform the OP that maybe there isn't anything wrong with their RV's V10 engine.