Might I suggest skipping New York and Boston with the RV and fly out there on a separate trip, renting a car and moteling it. Those two locations are a long drive from the rest of your itinerary and neither are particularly fun places with a Class A, especially if you haven't driven one quite a bit. Really, the same goes for New Orleans -- head there by plane and enjoy that way. You'll go a long way toward paying for those separate trips just from the fuel savings in not driving a Class A 5000 miles just for those places.
So if you can do those three locations as separate, fly-in fly-out mini vacations, that keeps the rest of your places in the western half of the U.S.
I'd agree with the above poster re: the temps in Death Valley in July, esp. in a rental unit. Also, unless your heart is really set on Las Vegas, there are cooler places to gamble if that's what you're looking for (how about the NV side of Tahoe?)
You need to secure reservations for the more popular destinations NOW. You already might have trouble with Yellowstone depending on the size of your rig.
