I think you'll enjoy 191 compared to the route you've already taken. It's wide open country with beautiful vistas. However, there are some ups and downs and gentle big curves but nothing like you've already be on to Yellowstone, Black Hills, etc. Have a great trip!
Full-Timed for 16 Years
.... Back in S&B Again
Traveled 8 yr in a 40' 2004 Newmar Dutch Star Motorhome
& 8 yr in a 33' Travel Supreme 5th Wheel