Graphics stutters, is my GPU dying?

Hi guys.
Quite new here, so hope you'll bear with me.
I've got some serious issues with my games, think it's the GPU, which is a Geforce 8800 GTX with 768 mb ram.
It started in Batman: Arkham Asylum, but so far it has also occured in games such as Borderlands, Mass Effect, and Fifa 10.
The game runs fine for 20 seconds or so, then the framerate drops to 2-4 fps, for 15-20 seconds. Then the stuttering goes away and the game runs fine, for 20 secs, then it starts again. As you can imagine, this is very frustrating, and I'm running out of ideas. It makes no difference if I'm staring into a wall with absolutely no action on the screen, or there is some heavy fighting happening.
I tried reducing details, AA, resolution, turning PhysX on/off, and all the other obvious things. I tried upgrading drivers for sound and video, removing drivers and reinstalling them, all to no avail. Now I've run out of ideas...
The strange thing is that for some games there are no problems whatsoever... I run Aion, Arma 2, Tropico 3, Red Faction Renegade and Majesty 2 without any problems, but the other games are just impossible to play.
So, please help me, I'm completely lost, and my brand new games are just lying there on my table, gathering dust...

 

I had an almost exactly the same problem with my old 8800GTX - the frame rate would drop to about 5-10 FPS for about a minute or two then return back to normal for the next 7-10 minutes and this would go on indefinetely in every game i tried playing. I later discovered that the card was overheating to about 112 degrees C under load and I had to RMA it. So, I'd suggest you check your card's temps using HW Monitor(CPUID) or RivaTuner(RivaTuner). Just leave them running in the background while gaming or running FurMark(FurMark: Graphics Card Stability and Stress Test, OpenGL Benchmark and GPU Temperature | oZone3D.Net). If your card's temps are normal(which should be up to 85 degrees C under full load if I remember correctly, but I'm not really sure), try it on a different motherboard and see what happens.