Can't see you doing Yellowstone and the Grand Canyon in one trip. Unless you want to drive non-stop and not see anything. You're looking a days of driving just to get to one or the other then the same to return. Now if you plan on driving around the clock to get there well maybe.
I probably don't drive as many miles a day as you will but last summer we drove from MI to the Black Hills. Then to Yellowstone and back home. A little over 3 weeks and we could have used more time. We saw a lot but there were things we didn't see. Honestly, as everyone else said, pick one or the other. There's enough to see and do and you won't have to spend the whole time driving. Try to cram in too much and it's no longer a vacation. It becomes a chore, rushing from one place to the other with no time to enjoy any of it.
