For what it's worth, we did our RV trip last summer and arrived at Glacier second week of July, just after a 6' late season snow fall.
Going To The Sun was closed to motorized traffic until the last day of our stay. Our Red Bus Tour was not canceled, but would be rerouting to sights off of GTTS, not ideal.
Doing a white water rafting trip on one of our first days there, our guide mentioned that one way to get up GTTS was by renting e-bikes. The pitch and duration of GTTS is like one of the mountain stages in the Tour de France, so riding a normal bike up it is not recommended unless you are a top athlete.
Lucky for us, I was able to score the last three e-bikes available for rent in the area.
We set out from Avalanche Creek at 10am in excellent weather and had an amazing, amazing adventure, "pedaling" all the way to the Pass.
I would not have wanted to do this sharing the road with motorized traffic, but doing this with the whole road to ourselves and other hikers and bikers was just incredible. What a way to see the sights!
The ride down was in a surprise rainstorm, cold, wet and windy, but it was all downhill: