OK, will chime in.
If Sept I would head to Moab - we will be there once again this Sept ourselves. From there we go to Capitol Reef which we love much more than Zion - although they are very different. We also like Bryce and will be there the first couple of days of Oct and then down to the Grand Canyon - ave lows for these places then is about 30-33 degrees --- sacrifice we make for the Fall beauty and photo work. And we hike - no 4 wheeling. Been to all several times - feel free to PM or email me if you would like.