I am a planner too, but it sounds like you left home without much time to plan.
Try US 191 from the Bryce-Capitol Reef-Arches-Canyonlands NPs to Grand Teton and Yellowstone NPs. You avoid all the Salt Lake City I-15 traffic and the higher elevations of the Unitas and Flaming Gorge are gorgeous, as well as cooler. You can also stop at the Utah Field Museum in Vernal for a couple of hours, especially if you don't have time to spend a day going out to Dinosaur National Monument (although the dinosaur quarry there is spectacular too!). We stayed at the Firefighter's Memorial Forest Service Campground near the top of the Uintas and would definitely recommend it. No hookups there, just water, flush toilets, and a dump, so you may need your generator.
A wonderful campground to try to get into at Grand Teton NP is Colter Bay on Jackson Lake. They have both FHU sites and no hookup sites--not cheap, but well worth it for the views. When you leave Yellowstone, try to go out through Cody and spend a day at the Buffalo Bill Center of the West. It's worth every penny!
If you do get into Colorado on your way home, take a look at my new blog for some inexpensive camping ideas and not-to-be-missed scenic attractions along the major US highways in the Colorado Rockies. The blog can be found
HERE.Have a great trip!