I understand what you'rw saying. To give you ome idea we were in North caroline in September. I know it's not Colorado (we lived in Arvada for 12 years). Black Mountain Pass is a 6% grade for 6 miles and curvy more the I-70 to the Tunnel. We started at the bottom at ~60 mph, and topped the pass at ~48 mph. No other coaches passed us for what that's worth. We crossed several passes in Montana, Idaho, and Wyoming with similar results. Of note, we tend to stay on interstates as much as possible.
Our grandkids are a bit older than your children 7,7,12 but ours don't get bored in our coach. They watch videos in the bedroom can move around while we're on straight roads, play cards, etc.
AZ lists several coaches at what look like reasonable prices. you might check out RTV.com.
Jim and Lynda, (Sophie, Jake, attack trained killer Shi-Tzus :-))
2003 Fleetwood Expedition 38N 2005 Saturn Vue