After reading all the posts, I have to say thank you to you all! You've never disappointed in helping us w trips!!
To address a few recurring comments:
We do plan on making the drive in 3 days - we do 20 hours straight through once a year to our Florida time share and have done many long trips so we'll be good there.
We've been to Mt Rushmore, Rocky Mountain NP and Grand Canyon, though we were at the South Rim, so we'll most likely visit North Rim this time too.
We are avid hikers, so that will be a large activity we pursue.
We're locked into these 2 weeks due to work. We've done Texas, New Mexico and Nevada in the same time frame, so we're familiar w planning around the heat. :)
Keep the suggestions coming! Thanks!