Gaming PC stuttering in games

I recently built a gaming PC late 2009, and from the start I had problems with it. Now every game I seem to start up stutters or pauses for half a second every once and a while. Here are the specs:

Intel Core i7 950 Quad-Core 3.06GHz
Cooler Master V8 CPU Cooler
OCZ DDR3 PC3-12800 Gold 6GB
EVGA X58 SLI
Western Digital VelociRaptor 150GB
LG Blu-Ray DVD Combo Drive
Cooler Master HAF 932 Full Tower ATX Case
EVGA GeForce GTX 275 Superclocked x2 (SLI)
Thermaltake Toughpower VGA Power Express 650W (Running both video cards)
Microsoft Windows 7 Pro 64-Bit
Mushkin XP-650AP 650W ATX Enhanced

So far I have tried:
- changing PCI slots
- running it with one GTX 275
- running different memory
- swapping out power supplies

I ran memtest, hard drive tests, OCCT and prime95. Everything is working properly except my CPU failed prime95 AND OCCT after 1 - 11 minutes on several cores each time. Could this be the problem? Any insight on how to fix this would be helpful.

You are doing OC ??

Tried conservative timings ???

Disable drive indexing? (right click on drive).

Search "Windows Performance Tweaks"

It has something to do with memory bandwidth, storage bandwidth or Video Drivers ...

... If you don't have the latest nVidia drivers ... GET THEM ... nVidia just "copped" to bad driver issues and the old "new drivers" were causing cards to burn up ... And I DO MEAN your 275 ! ROLL BACK, or UPDATE (if available).

= Al =

... right ... I defer to SS ... 'Cept for the video drivers.

Drivers,drivers,drivers - its always drivers. Update, rollback, reinstall,un-install. Whatever gets the job done.

Yes the RAM was manually set to 1600MHz, along with the timings. I'll run memtest overnight and see if anything changes.

Yep, the voltage was set manually as well to 1.650V.