Not recommended but you can run it. I've seen 13.5 on stock. It's best to have a 8" wide rim if you want anything 12.5" and wider. And it should fit stock, might rub at full lock.
And going to a 33" tire you do not need to regear.. I have 35s stock 3.55 and I have plenty of power. Now if I towed alot, or heavy I would definitely regear so I have more off the line power to get my load going but if not don't worry.