一个人开车,又要开车,又要看路,特别累，晚上才睡5个小时

I am quoting what you said on 车坛. Solo driver for 3500 miles in strange places?! Not a very good idea, in my opinion.

If you don't have time, send your friend to a tour group for Yellowstone, etc. after the holidays, if I were you.

Or otherwise, fly to Vegas (you might be able to find a better deal after memorial day) and drive to Grand Canyon, etc.