As soon as you leave the Phoenix area you'll have an uphill with curves for a few miles. Then it will be fairly level for a while until the downhill described below into Camp Verde. Then you'll have a long uphill to Flagstaff. It's steep and long but we've been on steeper.
According to the 'Mountain Directory for Truckers and RVers' (highly recommended if you're going to be driving mountain areas):
"from the south into Camp Verde, downhill 6% for 7 miles". This is the biggie for your trip. Downshift before you even begin the downhill. Don't try to slow down once you're into the downhill.