My experience is with US-400, US-166 in the eastern half of the state, and US-54 east of US-169. Then 400 again from Dodge City into Colorado.
US numbers highways in Kansas are usually pretty good, with generous lane widths, good shoulders, and passing lanes where needed. One thing to keep in mind for Kansas is the importance of "Keep Right Except to Pass" because the passing lanes are usually marked for use by traffic traveling in both directions.
Can't vouch for Oklahoma, the US highway system just hasn't been getting as much money, and many of the highways are still at 1960s to 1980s standards with 10-11 foot lanes, soft narrow shoulders sloping into a nearby bar ditch. I'll sometimes go a few miles out of my way up into Kansas to take US-166 from one place in northern Oklahoma to another, rather than use the northernmost Oklahoma highway (in this case, a state highway with even lower standards).
Tom Test
Itasca Spirit 29B