Agree with accsys, to try UT-9 from Zion to Mt. Carmel.I haven't driven UT-9 for a long while and don't remember how bad it was, but the alternatives I drove 2 years ago.
I think you'll find 14 and 20 challenging at 9% and 7.5% uphill grades and about the same on the downhill sides. Don't even think about trying 143 east from Parowan.
Try using Google Earth Pro to do a "Directions" mapping between the places you want to go, then right click the map and display the elevation profile. I use it all the time to see how much up/down a route presents.
