34 has some narrow, winding areas (it's not a big road) but you should still be ok, just take it easy. It's probably no faster a route than taking US 89 north from Montpelier ID, even though the latter goes over a higher pass. It's a bigger road & a nice, scenic drive either way. I'd give the edge to 89, though. We've towed a 34' TT over the 89 route with no issues.
2020 Toyota Tundra CrewMax 5.7L V8 w/ tow pkg, Equal-i-zer
2020 Lance 2375