Hello cat3corpus. Welcome to Android Forums. I encountered the same problems on a Rezound a year ago or so. Sometimes an upgrade will get the cart before the horse and things just don't run as they should. I would recommend backing up your phone and then performing a factory reset. I know it's a hassle but you'll be surprised at the improvements afterwards.
Before doing anything you will want to check out the discussion area for your phone. The other members that own the same phone will likely have the best advice for you.
Here is a link to that area:
Samsung Galaxy S3 - Android Forums
I hope that is the area for your phone. If not, open this link and then give your phone link a click: Android Phones - Android Forums
Best of luck to you. I am sorry you are having problems but very glad that you chose Android Forums for your support.