CloudDriver wrote:
...My suggestion would be to reverse the sequence to head west across TX to AZ and UT and work your way north to arrive in Yellowstone at the end of May to early June....
X2!
Late May to early June is a great time to be in Yellowstone. It will still be cool and some roads may still be closed, but most will be open. Better weather will be later, but it won't be getting crowded until late June. Early June is really a beautiful time of year in Yellowstone with lots of baby elk, etc. The main roads going into the park don't usually open until mid-April, if even then.