For some reason many times my game starts to stutter after 20 or 30 minutes of gameplay. I can fix this by Alt+Tab but sometimes is really annoying because I'm in the middle of a big fight and I'm forced to minimize the game because of this.

I play in Windowed Fullscreen mode 1920x1080 60 hz, 60 fps all the time except when this stuttering starts

I7 4770k
GTX 760 2GB
8 Gigs of ram
Win 7 64 bits