Your 90 Pace is going to need to be geared down on the steep hills as you have describe in your post.
I do not feel the heat issue would be a problem going down a hill going up it may.
I have a gas coach and its taken out of overdrive and I gear down to third and the coach will slow with the engine compression.
If its a real long grade may even put it down another gear and just touch brakes to keep it slowed.
If you do heat up engine the fan clutch will engage to cool down the radiator.
Here is a post on mountain driving
fo DP's that will have some info that you can apply in your gas coach.
Here is another threads on RV Driving and a Driving Course.
We were in Branson and could nor believe the hills in that area they sure didn't level them out.
Enjoy your RV and safe travels.