Stuttering, lag and freezing in BO2

Hello.

I just registered here so I'm not sure where I should post this issue or if it's the right website to ask for tech support.

So I have a GTX 670 from GALAXY and I've been a bit worried about its performance.

Whenever I play Black Ops 2, I always get a smooth 60 fps, on ultra with 4X TXAA anti-aliasing on a 1600x900 screen through a DVI cable.
Expect sometimes the game randomly stutters, and freezes for about 5-10 seconds, just enough time to get me killed and then goes back to normal for while.

MY SYSTEM:

Motherboard: GIGABYTE GA-Z77X-UD5H (1155 socket)
CPU: Intel Core i7-3770K@3.5GHz (Waiting for my H100i to start overclocking)-- CPU-Z tells me its core speed is 3.7-3.9GHz
GPU: GALAXY GTX 670--Strangely, GPU-Z tells me its GPU Core Clock is 324.0 MHz, GPU Memory Clock is 162.0 MHz. But maybe it says so because its idle.
RAM: 4GB, 1600MHz
Power Supply: Corsair AX850 (850W, obviously)

What can I do to try and fix this? Any help would be greatly appreciated.