I agree with, dont plan too much time for Deadwood. Hickoks grave and short walk about covers it unless you're there to drink and gamble.
I would prioritize the Little Big Horn Battlefield and the Cody Museum. Then youre near a Yellowstone entrance, you can exit Yellowstine on the Beartooth Highway. Look it up! Dont miss the Battlefield, Cody, and the Beartooth!
Safe travels,
Ed