You write that you are going to Glacier via Medora. Several are suggesting you drop down to the Black Hills. That is a LONG way south and then back if your destination is Glacier.
In September we did both Dakotas. Strongly suggest you stop in Medora for several days if time allows. The North Dakota Badlands (T. Roosevelt NP) at Medora are beautiful and there's a lot of stuff to do and experience: the Medora Musical, N. Dakota Cowboy Hall of Fame, etc.