Be sure you go with a professional guide because that area is beyond sparse. Carrying water is a must, this is very much a desert. I have driven through many times, going from AZ to Grand Junction, CO and each trip was different and very very starkly beautiful.
The Navajo are not the most friendly to the white man, they have very few reasons to love him. Some of the attitudes toward the Indians, I ran into while I lived in AZ were very reminiscent of the Old South back in the day. It was pretty shocking to an OK native because that's certainly not the attitude I'm used to.
This is an incredibly harsh area and uniquely beautiful. If you stay on the rez and are guests of the Dine, be respectful and generous with your tips, this is one of the poorest regions in the whole U.S.
While travelling back and forth from AZ to CO I got to be acquainted with a few folks on the Rez and found them to be very charming once the ice thawed. Love the area and I long to return when I can stay for a few days and do some serious exploring.
If you can get to Moab (about 180 miles to the north) you can do Colorado River rafting and enjoy some of the unique sights there too.