A few other sightseeing suggestions if you're traveling I-44/40 would be:
-Cadillac Ranch just outside Amarillo, TX.
-The Painted Desert in the north portion (north of I40) of the Petrified Forest Nat'l Park in AZ. I actually enjoyed this more than the Grand Canyon. Less visitors so you have more time to enjoy the scenery.
-Tucumcari, NM is a great pit stop. We took pictures at the retro Blue Swallow Hotel and ate at the Kix on 66 restaurant. Good food and they have a big parking lot in the back so plenty of space for bigger trailers and such.
-Lastly, make sure to stop and see the Wigwam Motel in Holbrook, AZ. They're still in use as a motel. I thought they were so unique.
Just some ideas...