UP doesn’t own much track in the SE. Here’s a map of their routes:
https://www.up.com/aboutup/Usguide/
I think that CSX and BNSF are big owners there, but I stand by to be corrected (sincerely). I don’t know much about RRs other than I like them!
We are big railroad fans from our days being stationed in Germany. We have taken most of the long distance Amtrak lines out west and really enjoyed the trips. Only the New Orleans to LA route has not been done so far. The Empire Builder across the northern plains was my favorite but crossing the Rockies from Denver to SF was great too.