APK -
Leaving from the west coast, you will have plenty of time to get through the Rockies without the need to rush.
Why rush, anyhoo? You are having dessert first.
Everything that was already open in a semi-Covid year will still be open in Yellowstone.
Please go the extra few miles to Jenny Lake in Grand Teton National Park. It's really worth it.
You might have one litte snow - maybe a day off. You will have some chilly nights.
You will have more moderate temperatures in the Great Plains - way more enjoyable.
Then you'll hit the Appalachians in early to mid fall.
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60 days is pushing it.
90 is slow, 80 is moderate, 70 is quick.
75 days would get you back easy by the end of October.
Which is about when the good touring days start to fade away.
Have a great trip! - J