We returned 6/22 from a 3 week trip out west that took us 1000 miles down I-40 from Alabama to Santa Fe and back.
On the way out we crossed the Mississippi at West Helena to avoid Memphis. Good roads from N AL to I-40 at Brinkley, but very desolate - plan your fuel stops.
Coming back we decided to shoot the curl and try to pull thru Memphis for the first time. 1PM on a weekday and it went fine.
But to your point, I-40 thru Oklahoma is consistently bad just about the length of the state. Last weekend we found a couple of very rough spots on I-40 eastbound between Little Rock and Memphis, but nothing like Oklahoma. The signs say the construction around Forest City is finished, at least eastbound.
Can't speak for westbound from Memphis to Little Rock because we didn't go that way, but if I was coming east again this weekend I'd go thru Memphis again.
Just my 2 cents.