[LS short box]

Maybe your plans aren't going further east and north but the Tetons and Yellowstone are pretty cool. Best in early to mid May before all the tourists show up. I lived in Bozeman as kid and our Sunday trips were a loop thru the park. Around the lake and Eden Valley. Then as a bonus the garbage dump near West Yellowstone watching the bears grizz and blacks going thru the garbage
The deer/elk/buffalo/moose/bears and maybe even a wolf will look a bit scruffy in May but still fun to watch.
The Beartooth highway is very cool but may not be open in early May.