Best roads between Palm Springs CA and Prescott AZ

There is a length limit of 40' on US 89 South of Prescott. It isn't a long stretch of switchbacks, but it takes forever and would be a big climb, even if you disconnect, which you would need to do, heading north to Prescott. The outcrops on the inside of the turns jut out enough to make it quite hairy in a motorhome. We did it going south in a 38' DP without a toad and it was hair raising, not to mention incredibly slow. 15 mph a lot of the time.