Hi Lauren
So glad to hear you are coming to the IRG
Sandi and I are looking forward to meeting you after following your build here on the Forum.
When I started reading your post, while looking at your map..... I got excited about you being so close to us on your way there, but then I read 6 days??
We drove home from the UP of Michigan on a similar route in 2012. It took us 5 days...and we were driving!!!

I had my 46 Stude PU with nothing attached, and we were consistently averaging 85 mph.
I think you might want to take more time and smell the roses along the way. There are some great things to see along the way, I am sure you are going to start getting some wonderful suggestions.
This will be a trip that I am sure you will remember forever, so find a way to take more time to do it.
In stead of staying on I 90 after Missoula....200 is a much nicer drive up to Sandpoint.
Oh there is just too much to tell you in this post.
Also, get your passport before you come so you have a Canadian option. B.C. is worth it!!!
We are going to the IRG also, and I am currently planning our trip down??? We will be taking our time and know almost all of the routes.
I would love to help you with your travel plans through the Pacific North West!
Lets keep in touch.
Good Roads
Brian & Sandi