US95 north out of Lewiston does climb significantly, though at modern highway standards. Other routes out of the valley climb more gradually. Clarkston is just across the Snake, so there's no climb. US12 on west does climb to the same area plateau level, but takes longer.
I suppose I shouldn't mention 128/3 south. It's more direct (half the miles cf to Walla Walla. But there is the big twisty drop to the La Grange River (aka Rattlesnake grade). Overall amount of climbing is less.
Lewiston is 700ft elevation, lowest point in Idaho, Joesph is 4000+ ft, so you'll climb regardless of route.