i'm from Delaware way back when.
Appalacians south > NW Alabama > cross Mississippi > toward Little Rock > ride a few days in the Ozarks (we have a map) > exit out of SE Oklahoma.
at this point either slab it across to New Mexico or ride down into the Texas Hill Country (we have a map)
the northern alternative is RT 2 at the top of the country.
Google Maps - terrain view is a great way to look for terrain change and thus fun roads.