'Steep' downhill grade into Hurricane. 55 to 45 to 35mph. The highway drops you right into a residential zone. It isn't a big deal though, plenty of loaded semis doing the same thing. 
Climbs? North toward Page you have 'The Big Cut' just north of Bitter Springs. There is a passing lane the whole way up so take your time if needed. Then as you get closer to Page you have '12 Mile Hill' which is a short downhill with some curves; not even sure if it is worth mentioning, other than just watch the caution signs for speed. 
I cannot think of anything else for that particular route for going to the West Entrance of Zion's.
If you were to choose the East Entrance however, a few miles north out of Kanab has a not steep but few mile long climb. It is quickly followed by a long sweeping curve downgrade into Mt Carmel Junction.
For any of the above, your Winne is plenty capable. Every grade I've mentioned is considered a normal route for over the road trucks. You are over thinking this.