Mt Rushmore, Yellowstone, Cheyenne

If it was me, I would take the time you are planning on seeing Cheyenne and spend it in Grand Teton, which you will probably pass through on your way home anyway, unless you go over Sylvan Pass, then you need to stop in Cody to see the Buffalo Bill Museum. Easier pull through Grand Teton and you could park in the Colter Bay campground while you are there, the sites are all first-come, first-served. Get there around 9:30-10:00 in the morning just before checkout time and you could get a good spot. And you are right, three days in Yellowstone will allow you to see the high spots, but it really is a big place and, unless you don't like to get out of your car, you'll only get to see the high spots. Since you have two weeks and are going to spend six of them traveling to and from the parks, I would suggest that one day is plenty to see Mount Rushmore and Crazy Horse and then drive towards Yellowstone and have a great time. Three days in Yellowstone, after one day of travel to get you there would leave you a couple/three days to see Grand Teton and down through Dubois to Lander and Rawlins to I-80 and then home.