The Tuba City Truck Stop Cafe serves a good Navajo taco. We were through there 4 years ago and the experience was consistent with my first visit in 1986. One caution: do not order the vegetarian taco. My travelling companion did and it was a can of cold beans on dressed fry bread. It was inedible.
Don’t worry about finding it. Just head down HWY 160 and take the exist for Tuba City. It will be off the main road on your right.