I would suggest you first get a good road atlas and study each state you want to explore. Highlight the attractions such as Grand Canyon, Yellowstone, etc. and then make your route from there.  To save your precious time, I'd skip the Midwest states for exploring and concentrate on once you get to Arizona or Colorado to begin your trip in earnest.
Until you reach those states just take the interstate and plan on no more than 400-500/day. It will be grueling and boring.  Once you get off on the secondary roads and start exploring you will be traveling much slower - 200-300 miles/day will be tops.
Here is a good RV park site that many RVers use. Pick your nearest town to the attraction and start researching.
Your trip can be done in the time you have. If you can't see all you want or can't stay as long as you want you'll just have to come back for more!
http://www.rvparkreviews.com/