My Son works at Glacier, and I was lucky enough to spend a week there with him the last of August. Glacier is one of those places that just makes you say, OMG, it is awesome! Going to the Sun Road is beautiful, and that is what Glacier is all about. So, definitely plan on doing that. I would plan on late July or August, temps are nice then too. Don't stress about driving it, take the Red Bus tour. We took the Crown of the Continent tour from West Glacier to East Glacier, and were able to just sit back, enjoy the scenery, and let someone else do the driving.