Download EVGA Precision X and keep things at stock clocks, make a custom fan profile (mine goes up 10% or so for ever 5 degrees roughly, at 70 degrees Celsius its at 100% fan speed) and also go into the on screen display monitoring and enable core clock, temp, and voltage in on screen display and start gaming, watch the temp, if its not over heating and all of a sudden your core clock drops dramatically, you have the same issue i did.
To resolve that issue, use EVGA Precision X to raise the Voltage of the card to anything over your current stock setting (i personally have it maxxed, but thats because i have it OC'd max is 1.088 volts)
That should fix your issue.
My EVGA GTX460 was having several issues, i dont know if it is an issue with the Fermi based cards or if i just have a finicky card, but doing what i have mentioned has worked so far.
<message edited by gosna on Thursday, July 12, 2012 2:39 PM>