GPS is for suckers (unless you're a city you don't know - but state maps don't go to that kind of detail) - whatever happened to the good ol' days of ending up where you end up? I drove cross-country & back over the course of 2 months when I was in college & navigated by highways signs & rest areas. We had a AAA map of the US so we could figure things out, but mostly, we asked locals for ideas & cool places to go.
One thing I recommend if ever doing a cross-country roadtrip is to follow the dotted roads - which are generally the scenic routes - much more interesting than highways & less crowded - there are some sights that I saw in Colorado that were just amazing because I stayed off highways!