Possible Graphics Card Issues

[Panda Bear]

I've got a pair of GTX 580's which are both well under a year old and i've started seeing a real decrease in playability in games, games like Dirt 2 used to be perfect with full settings, as you'd expect, but now it stutters every now and again and every few races completely freezes.

this happens in most games but dirt is where it happens the most. i have a temp monitor running in the background and the cards never seem to get above 55 degrees, a fairly aggressive fan curve keeps them down.

i've tried re-seating the cards, removing all graphics drivers and reinstalling games but nothing seems to work

i even tried old AOE III to see whether happened on non-demanding games which showed the game slowing right down at certain points then speeding up to account for it.

Both cards are running at 880Mhz GPU, 4200Mhz Memory with the latest Nvidia drivers.

any idea's about what the best thing do do from here would be?

cheers

[+PeterUK MVC]

Have you tried putting the CPU back to stock speeds and trying one GTX 580 at a time to see if one might be faulty?

[Panda Bear]

is there a tried and true method for doing that that would rule out all other components being the possible cause