We usually put 15,000+ miles on our coach each year. Most of it out West. For most travel, the hills are moderate and no sweat at all for our 8.1L gasser with the Allison transmission. From time to time we will come across a hill that is steeper than the rest and I am limited to 30-40 MPH, while towing our HHR. These usually are only a few miles long but sometimes can be a 10 mile climb. I would say that in the course of a year, we might run into 50-100 miles of these steep climbs, or less than 1% of the total traveling that we do.
Basically what I am saying that unless you really plan to travel a lot on steep roads, don't worry too much about it and don't spend a lot of money for something that will happen very seldom. I have never read on this forum where someone failed to make it up the highway in their coach because the road was too steep and their engine was too weak. Sometimes it does take a little longer to get to the top, but it will not happen very often at all.