We took US 36 from Hannibal, MO to Denver a couple of years ago. We were towing the 5th wheel, so in no hurry. It is 4-lane across MO and ok 2-lane across KS. Lots of ups and downs in western KS, but no long grades. We spent a night at a vacant lot with FHUs across US 281 from the football stadium in Norton, KS. Cheap and "the best restaurant in town" was across a side street from the "RV park". One of the strangest places we've stayed in so far!
See my blog at https://2fanrgs.blogspot.com for route, campsite, and not-to-miss sightseeing suggestions in Colorado.