Unless we're trying to make time to get from point A-B, we avoid the Interstate as much as possible. A couple changes I would suggest.
On your way through Cooke City, stop at the Miners Saloon for Lunch or bottle of water. Sitting next to the bar, is a statue of what Lawyers become
At Red Lodge, MT take 308 East to 72 North to 310 South to 14A (a little detour to Shell Falls is worth it!) to I-90. You can backtrack to Custer Battlefield.
From Sheridan take Hiway 14/16 to Gillette.You'll be able to bag a Grand Tour location at Ucross! Be sure to stop in Spotted Horse for a burger. For a bonus, tell me who the famous person is that stops there on his way to Sturgis every year?
From Devils Tower take 24 East to 34 into Bell Fourche, the Center of the Nation.
44 & 18 are much better than I-90 crossing South Dakota.
We've ridden all these roads several times. I promise, you'll be impressed!
With everyone heading West this summer it may get crowded, Marlene & I are going to the Coast. We've tried bagging Crater lake 3 times, once making it to the Ranger station only to be turned away because of snow. Hopefully we'll get it this time.