I have none that quite meet the OP's criteria, but I have made three cross-country trips that barely miss:
1) McCall, ID to Portland, ME and back in 2007 with a few friends from high school after our freshman year of college. We stopped to see various people we had met at our respective universities all the way there and back, essentially partying our way across the country and back. It was a fun two weeks. We did cheat on the way out and go through Ontario and Quebec.
2) Deer Lodge, MT to Woodruff, SC and back in 2014. Woodruff was not the destination, but was the furthest I got from Deer Lodge on my way to the 2014 St. Louis meet. I did this trip nearly completely off-interstate once east of Billings - heading through the UP, then snaking my way down to SC and back to Missouri. With the exception of a few (< 100) miles where the route I was driving was concurrent with the interstate, I drove no interstate mileage outside of Montana.
3) Charlotte, NC to Boise, ID in 2001. I was too young to drive, obviously, but my Dad and I took a Jeep Wrangler that my older sister had been using at college at UNCG back to Idaho when she bought her own car. It was a soft top 4-cylinder Jeep Wrangler with no A/C in the middle of summer, which made for a reasonably miserable trip. We drove I-70 across Missouri with bags of ice on our lap - my Dad finally had enough of the interstates when we got to South Dakota (we took I-90 across SD), and we continued back through Yellowstone.
I've made more trips from Idaho/Montana to the Pacific than I can count to combine as a single "cross country trip," so I won't list those.