We did the Columbia river route on our way home from the Olympic Penn. on 84 to Salt Lake City and there was nothing challenging about it. I had a 30ft. trailer with me and had no issue at all. Not the same time of year but the road is not the infamous mountain pass kind of road at all.
Heading south on I-5 into Cali. you put yourself into major cities to get far enough south to cut over east. Out of SLC take 80 east, no mountain passes like on 70 in Colorado, Vail pass is 10,000 ft. altitude.
Nashville has Broadway street with the music bars and country singer museums. Andrew Jackson's home, The Hermitage is just east of downtown and worth the stop. The museum is very interesting and the home tour is good too. Weather here in TN in April is, or should be pleasant with the trees and early flowers budding out. Depending on how long you stay in Nashville you might consider a day trip down to Lynchburg and the Jack Daniel Distillery, or just head down to Tims Ford State Park for a couple days. Due to COVID they have suspended their tours though so who knows if they might resume by then. The bottle shop is still open though. Not far from Lynchburg is Tullahoma where the Beechcraft Heritage Museum is. If you like aircraft this is a wonderful stop.