Hey Gene - Labor Day weekend is usually the "last big weekend" in Glacier before things start shutting down crowd wise. You'll still find the basic staple places open but the touristy shops usually are starting to board up for winter shortly thereafter (a lot of their workers are high school or college kids). Some of my best bicycle and hiking times in Glacier have been in September, even early October. The risk that you take, the later you wait, is that the weather will get cool up high on the Sun Road and it'll occasionally drop some skiffs of snow, though they keep it plowed and it melts off pretty quickly on a warm Fall day. You'll not find many RV's and big trucks on the Going to the Sun Road because they limit the length of the vehicles due to the tight road/turns. They occasionally have some road construction going on, but nothing that would deter you from taking the road. Doubt they'll be working on it much in September, but worth checking in advance. Call Glacier Park Headquarters at West Glacier/Apgar and they can give you the scoop. It's an amazing ride. If you have the time, go north up to St. Mary's, then 20 miles further up to Many Glacier, then up to Waterton (another hour) using the Chief Mountain border crossing into Canada. You won't be disappointed! Waterton's a neat little town with a fantastic mountainous backdrop. Short 9 mile ride up to Cameron Lake above it is a nice short sidetrip as well. If you're camping, let me know and I can point out some good camp spots, though some campgrounds will be closed that time of the year. I'd bet you could find some indoor lodging - safer from the weather and bears that time of the year.
Holler if you have any other questions on W. MT. Would be glad to provide suggestions for great rides/places the check out.
PS Make sure you leave your gators down south, we have our hands full with the grizzlies.
