I'll also ditto the 50 mph rule.
Another big suggestion is to visit a FEW places and take you time at each. Newbies tend to want come up with a long list of places which means they spend most of their vacation driving from place to place.
We used to pick a central location and do day trips from there.
So decide how many days you have.
Plan ob 5-6 days each way for Utah. Eastern Colorado is a day less but you are more limited in parks, Rocky Mountains and Great Sand Dunes. I think RMNP may require tickets now. Better check on that.
Taking I80/90 west will run you thru the South Dakota Parks: Badlands and Rushmore with some other minor stops.
Utah: Zion and Arches are absolutely mobbed, packed, too many people. Zion has shuttle tickets you have to buy online. Arches lockes the gates when full, Zion will keep you waiting in a traffic jam for hours to get to a parking lot which will probably be full.
Capitol Reef has fewer people. Canyonlands also but you need at least a high clearance vehicle to drive the roads. Cedar Breaks is little visited but only open 3-4 months a year.
AZ: Many indian ruins parks but the are hotter than Hades in summer. So are Zion and Arches BTW.South Rim of the Grand Canyon also flooded with mobs. But cooler. North Rim has fewer people and is cooler yet.
Yellowstone is huge and has a lot of people. It is cooler, but expect in park traffic jam. Glacier seems to be getting mobs and requires difficult tp get tickets.
And lets not forget the big issue, where will you stay. Lodging/camping around the great parks needs to be reserved six months or more in advance.
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