Why are my iTunes TV Shows and Movies running so slowly?

I purchased a bunch of Viva la Bam episodes and they are running but like every 30 seconds the screens freezes and then the sound turns off. Then it runs really quick to catch itself up and then the cycle starts again. It's starting to really piss me off. I'll only be really itunes and the CPU will be at like 10 percent at most. I almost have 66% of space left on my hard drive, so it's not like my computer is overloaded. My internet runs fine. I don't understand what's wrong. Please help!