The 6 trips totalled about 3-4 weeks each. We would pretty much drive a long day on the first 700-900 miles then slow down to maybe 500-600 for the second (you gain 1 hour each day driving west!) then really start the sightseeing etc. I had planned route/places to stay each day. In the 80's it wasn't as easy to locate all the info. For the first trip I picked a few points along the way that we always wanted to visit - The
Alamo, Carlsbad Caverns, Grand Canyon DL (of course) Sequoia NP, Rocky Mountain NP, 4 corners, Mt Ruchmore. I looked at the map and plotted the course that allowed for other sites to fit in (I had a 50 states book)
Getting back to your question, Yes we have driven on I 80 (I actually think I 70 is a better ride) for portions of the trip between NJ and Chicago area. Most times we either went up north to 90 (more of the sites we wanted to see as well as less traffic) On the 6 trips I think 80 was the one interstate we used on either a west or east drive for that portion. A couple times we drove through NB as well. We really never drove the same east/west route on the same trip either. On NP we visited on all but 1 was Rocky Mountain NP in CO, I think my favorite overall. I love the area and mountains!! We have been to Yellowstone, Grand Teton, Glacier, Badlands, Olimpic, Redwood, Kings Canyon, Mesa Verde, Shennandoah, Smokey Mountain, Black Gunnison, Devils Tower, Wind Cave Saguaro, Zion, Bryce to name some of the most known. There are MANY along the routes cross country as well as many little neat places like Wall Drug Store and the Corn Palace in SD!! SD is really a neat state along with Mount Rushmore, Wind cave, badlands and Deadwood there is a lot to see!! Devil's Tower is about an hour away as well!! Just so you know we have done many east coast shorter trips and concentrated on the midwest and mostly the mountain west for the cross country trips. Any other questions, please ask. It's so much fun to plan and plot the trips. I actually make binders now for the trip with coupons/info in each divider. I contact each state and many smaller towns for all their free info as well as the National Parks and put the info along with place to stay and route in the binder. It's a lot of fun.