It's a very good highway and the only place with a long descent and uphill is between Show Low, AZ and Globe. You'll have the Salt River Canyon to drive through for about 10 miles or so. It's very doable with any size RV and many, many RVers drive it. Just get into low gear before you begin the descent - not in the middle of it. You'll then reach the river and begin your uphill to Globe. It's an absolutely gorgeous drive!
You didn't say where you're going from Globe but if it's into the Apache Junction/Phoenix area you'll have another descent around Superior, AZ.
From 60 at Show Low another way to get to Phoenix is to take 260 to Payson and 87 south. Again, you'll have another long descent into Phoenix. Everything is higher elevation than Phoenix so there's only one way to go and it's down.
Even taking I-40 to I-17 into Phoenix is a downhill.
Have a good trip!