San Diego to Oshkosh

I just did that trip in 2009, but I left from Northern Cal so we took I-80 all the way and made it in three days. Then took two weeks coming back and went over the north back through South Dakota and the northern states.

If I were leaving from San Diego, I'd probably follow the old Route 66 as much as possible just because I've never followed it before.

My son and I did a trip from San Diego to Pittsburgh. North on the 15 to red rock canyon, Las Vegas. ZIon and Bryce canyon, up to Yellowstone and headed west. Cody WY stopped at the Cody gun museum, Mt Rushmore, Crazy Horse. We tried to stop along the way at scenic or national parks. Before we left we purchased a park pass that covered the admission. The route will depend on what you want to see, or are you looking for the shortese route?