We will be doing somewhat the same drive in October. From Afton we're going via Evanston, WY and UT160 to Heber City, then UT40 east to 191 to I-70 at Green River. We'll then pick up Hwy 24 to Hanksville, UT and 95 to Blanding, UT. Then 191 to 163 into Arizona and 160 to Tuba City, AZ. Then AZ89 to Flagstaff. That's where our trip will be different from yours.
So...from Flagstaff you could take I-40 to Ash Fordk, Exit 144 and pick up Hwy 89 to Prescott. Instead of staying on 89, pick up Skull Valley Hwy. to Kirkland (a much easier drive than 89 at that point) and then you will be heading to Congress, AZ. Continue on 71 to Hwy 60 and take that into Quartzsite. It's all a very scenic drive. Many wonderful places to sitesee along the way and great boondocking opportunities if you do any. Depending on what you have and haven't seen in Utah, you could stop at some of the southern Utah national parks. We've done all the national parks multiple times so this route will have us seeing a few new things. Have a good trip!