From Flagstaff, take Hwy 89 north into Page and west to Kanab. We've done this multiple times. There are no big uphills or downhills - just moderate ones.
89T was a temporary road made to carry traffic when there was a landslide on 89 which closed the highway for about a year. 89T is o.k. to drive though but 89 is now open.
I recently heard that 89A was closed because of a big rockslide during recent rains. I'm not sure if it's open yet or not but that would be another way to go. Check out the condition just before you go. It would involve one big uphill and downhill around Jacob Lake but it's very scenic and many RVers drive it. We did.
Basically, RVers and semi trucks drive all the routes. Just pick one.