I live near Sedona AZ and drive from Arizona to the midwest or east coast nearly every year towing a car hauler. The steepest climb on the entire trip is always the I-17 grade from Camp Verde north to Flagstaff. It is a good road, just a long climb.
The other uphill grade for you headed north on I-17 will be north of Black Canyon City, and then headed north you'll have a downgrade just south of Camp Verde. None of these grades are terrifying, just hard on equipment.
I echo the thoughts about I-40 near Flagstaff. The AZ DOT should be ashamed of themselves. Another stretch that is bad is I-40 eastbound just west of Seligman. They've fixed most of it now, but there are still some bad sections. In my previous Class C I would lose at least one front hub cap every time we drove that stretch. I finally just quit buying replacements.
I-25 between Santa Fe and Walsenburg, CO is one of my favorites, which I guess is the way you came down to Az.
2004 National Dolphin LX 6320, W-22, 8.1, Allison 1000, Front/rear "Trac" Bars & Anti-sway Bars, Sumo Springs, Roadmaster Reflex Steering Stabilizer, 2005 PT Cruiser Toad