Most of these people have been giving good advice. My advice would be to cut back on how far you will go & contrate on what you want to see, 3 weeks or 21 days is long enought to have a nice trip but if you traveled 300 milles a day you could cover 6300 miles but wouldn't have much time to see the sights or enjoy them. Pick out what Nat Parks you want to visit then decide how long you will need to enjoy them. Take Yellowstone which you talked about to really see & enjoy I would plan at least 3-4 days maybe 5 if you wanted to tour Grand Teton N P which is just south of Yellowstone. You know what you want to do just remember take your time don't try to cover too much ground. When you get that far along in your planing let us know where you-all will be going and maybe we can point out things in that Park or area

billy bob