The Payson route is very scenic, especially HWY 3 (Lake Mary Road) from Clint's Well to Flag. (Watch for elk in the late afternoon / early evening!)
Most of the grade on 87 is four-lane and not much different than the grades on I-17, HOWEVER there is a short stretch of two-lane climbing out of Payson to the top of the Mogollon Rim that is two-lane and a bit twisty-turny. Not sure what that would be like with 70' of rig. Check google maps for a visual.
From the top of the Rim on to Flag is two-lane but smooth sailing.
