Stop in Amarillo and visit the smaller version, but still magnificient, of the Grand Canyon.
Palo Duro Canyon is awesome, and underappreciated. I highly recommend you spend a day or 2 there.
OKC has the National Memorial and I 2nd the visit of it.
While in OKC you would be amazed at the National Cowboy & Western Heritage Museum. The art work is fantastic, there is so much there to see, it deserves far more recognition.
If you run I-40 west from Amarillo, take the very 1st New Mexico exit and stop to fuel up, take a break, eat, whatever, at Russells Truck & Travel Center. Owner has an amazing car and other stuff museum that is absolutely free of charge. I always stop there, restroom break, etc, and wander through it. It's another under-appreciated gem.
If you want to stop in Albuquerque, the National Museum of Nuclear Science & History is amazing, too. It's just off I-40, catty-corner from a Costco. I always stop here too when traveling. You can google it or check out on Youtube.