A V10 E450 Class C from Thor or Forest River will come with a 7500# hitch stock, and all of that is usable as long as your tongue weight doesn't overload the rear axle. Tongue weight is probably the biggest challenge for motorhomes.
A diesel class C will cost substantially more, and come with many more maintenance headaches, all for an extra 2,500 pounds of towing capacity.
If you can hold out until fall, the E-series will be getting a 6-speed TorqueShift transmission, which should help with pulling power in the mountains.