I see you've changed your next stop from Custer, SD to Jackson, WY, so I'm not sure if my suggestion will be applicable...
As a native Coloradan living in South Dakota, I make the drive between the two A LOT. I love to drive through
Guernsey, WY and stop at the
Oregon Trail wagon ruts and other related sights.
Also, about 12 miles outside of Guernsey is
Ft. Laramie National Historic Site. They are still in the process of restoring some of it, but there is a lot that is already restored. It is really awesome to visit because it's kind of out there by itself and you get a real sense of what it would have been like to be so isolated from other people.
