we did your proposed route except in reverse a few years back. We went from colo springs to the north stayed at the KOA in Casper then went over to thermopolis wyo (if you like hot springs) then went to the north again to custer NM/battlefield. Over to yellowstone from the north and down to jackson where we day tripped to the Tetons and the national elk refuge. Great tourist info center in jackson. from there we went south over into Idaho. We plan to return to the hot springs just west of the state line. the route south took us to SLC and then down to bryce and zion. we then went to GC and then home. Have never been to glacier that is on the to do list. When we went to rushmore we found little to keep ya there unless you want to be tourist and go to the tourist traps like walls drug or over to sturgis and the environs. Lots of pronghorn to see as you go to the SW.
There is supposed to be a good park for theodore roosevelt in the dakotas not far from rushmore not sure, might be a place of interest.
