Well I've been posting on various forums and now have a tentative route planned with the help of feedback from some very helpful people.

We'll fly into Salt Lake City, stay overnight.
Drive up into Idaho - maybe Idaho Falls to stay over.
Drive up the western side of the Grand Tetons which we've seen before but only from the east - stay West Yellowstone.
Drive through the northern edge of Yellowstone Park and out along the Bear Tooth highway to Billings Montana.
See the Little Big Horn Battlefield and stay in Billings again.
Drive to Great Falls.
Drive through Glacier National Park along the going to the sun road - stay in Kalispell.
Drive down to Sun Valley / Ketchum stay over
See Craters of the Moon National Monument and stay in Ketchum again.
Drive down to Salt Lake City.
Fly home or maybe fly to Vegas for a few days before flying home.