Effy,
A suggestion: go to New Mexico and Colorado; save the far west for another day. Years ago, I took the only 1 month off from my work I ever took before retiring, to take our son on a western trek (from Chapel Hill, NC). We drove US 40 by car to Santa Fe, met up with my parents and tent-camped along with their little 5th wheel. In that month, we did Santa Fe, Bandolier Natl Mon, Taos, Chaco Canyon, Mesa Verde, Durango, Coal Mine Pass to Montross, and then headed east on US 50, diverting, via Leadville, up to Boulder, Rocky Mt. Natl Park, then home, via US 64. It was a most fabulous trip for us -- we had plenty of time to see each place at a reasonably unhurried pace, and you could easily shorten the route to 2 - 3 weeks.
One of the things we really enjoyed was being on the Colorado Plateau in August -- every day about 2:00 we had an afternoon thunder shower. It's their monsoon season, and the weather is fabulous!
I think the key is to plan a trip you can enjoy without hurrying, for the period of time you have available; don't rush it -- it's supposed to be a vacation!
Bon voyage!