Hi there,

I did a similar trip in Sept 2003. Day 3 looks a little aggressive to me if you really want to hit both parks. Day 4 looks fine, particularly if you can't do a ton of hiking.

I highly second the recommendation to visit Kodachrome, Cedar Breaks, and Coral Sand Dunes. I also highly recommend both parts of Zion, the lower canyon and the upper hills. Most people just see Zion canyon. I really enjoyed Kanab Utah as well.