Audio & Video Syncing is Choppy

I have a:

Macbook Pro, 2011.

16gm of RAM, 1333 mhz

OSX Mountain Lion.

Using iTunes v. 11.1.1

For the last couple weeks, my video purchases from iTunes are playing back with choppy video & audio syncing on full screen mode. It gets to the point that it's impossible to watch/listen to.

Anyone else having this problem or know a solution?