We used route 36 across MO and KS a few years back on the way to Great Sand Dunes in southern CO. Did not drive 36 in CO.
Route 36 is 2 lane across KS and a relaxed drive. We stopped at Prairie Dog State Park near Norton KS for an overnight. If you are interested, there is a Pony Express station in Marysville KS.
Route 36 in MO is a divided highway and another nice drive.
For your consideration, when heading west this last May we used route 30 between Mansfield OH and Van Wert OH. A nice divided highway with few trucks. We then used route 224 to route 24 across IN and on into IL. Route 224 is 2 lane and route 24 is divided highway as far west as Logansport IN, then 2 lane on west. This route avoids the toll roads in IN and OH as well as the crazy traffic on I80 around Chicago. We went through that traffic on the way home and won't be doing that again on future trips.