The flashers make me cringe a bit. I'm not quite convinced slow should come at the expense of safe driving.

Not sure about Provo / Salt Lake (the interstate may be the only option there). Personally living in France, so if I'm not pressed for time, I go off of the highway completely and either drive on "Nationale" (kind of a free / slower highway), or just let the GPS pick some more scenic route. There are plenty of nice rural corners around that are often worth a few minutes of a detour.