Driving my car across the country later this month from Boston to Seattle, wanting to definitely stop by Niagara Falls, Mount Rushmore and Yellowstone for sure, and planning to do it in about 5 days. Do you all have suggestions on how I should plan hotel stops for the nights? Thank you very much!
I did US 20 from Boston to Oregon, and then took interstate 90 from Seattle all the way back a couple years ago. I didn't take it slow at all on 90, I drove as far as I could each day and it took 5 days, you will not have much time to spare if you want to be properly rested and avoid night driving. I'll assume you are moving or something and aren't willing/able to take extra time. Probably dedicate what time you have to Badlands, Black Hills, and Devil's Tower.
My itinerary was like this (opposite direction from your trip, of course):
Westport, WA through Seattle to Butte, MT
Butte, MA to Wall, SD with time spent at Devil's Tower
Wall, SD to Wisconsin Dells, WI with time spent at Badlands NP
W. Dells, WI to Ashtabula, OH, shortest driving day but was still over 9 hours
Ashtabula, OH to Boston, MA