We have done the route from Missoula north. I believe it is 93 up to the west side of Flathead Lake. We were towing in a 36 ft Itascal Horizon. Not a bad road back then, but pretty crooked if you are trying to make time. Road follows the lake shore pretty much all the way past the lake.
In Kalispell we went US 2 through Hungry Horse. We stayed a few days in West Glacier and did day trips across the top to the east side of the park. In August there was still a lot of snow around the visitors center. Streams were full and running fast.
I believe the Going to the Sun Road has been re-done since we were there, adding width and some barriers in places.
I might call the pakr and make sure the GttS Road is open if that is one of your objectives. There is a length limit but we were OK in the Honda we were towing at the time. The Red Buses were running, but I preferred my own driving rather than riding with some guy I didn't know or how well he handled a loaded truck
horsedoc
2008 Damon Essence
2013 Jeep Sahara Unlimited
Blue Ox tow