I don't know if you have specific reasons to visit cities like Vegas, Denver, and SLC, but if not, there are far, far better destinations than those places.
Antelope Canyon and Page AZ will be incredibly hot in late June/early July. Antelope Canyon is impressive, but Page not so much. Have you been to Zion and/or Bryce? Bryce is higher in elevation and much more tolerable the time of year you will be travelling.
Have to agree with skipping the Black Hills. Long ways from home and you'll have to pass up on some amazing scenery.
If it were me for this time of year and with two weeks, I'd consider places like Durango (narrow gauge railroad is great), Salida through Leadville, up through Estes Park, up to the Tetons and Yellowstone, then back home. One can plan a route to these destinations and only travel over some of the lower/easier passes in Colorado.
But your limiting factor will be your late date in making reservations. For many places, the first week in July was booked many months ago. It's a tough week to even try to boondock as places are generally full for the whole week of the 4th.
Just my two cents worth.
