Things to visit on the return trip from Alaska

Personally, we wouldn't spend a lot of time siteseeing in the lower 48 on the way up to Alaska such as Yellowstone, etc. Save the major siteseeing on your way up for Canada, Yukon and Alaska - places you probably won't go often.

Then on your return, hit the lower 48 sites. You may find the weather better in late Aug/Sept and crowds lighter. Plus, you may be exhausted from the Alaska trip and just want to head home. You can easily spend three months once you cross into Canada.