This may be a stupid question, but have you checked your temperatures on your graphics card? nVidia's software should have something that lets you see. If you see that it's too high after gaming (idle doesn't matter as much), try downclocking the card a good bit using Coolbits and see if it fixes the issue. If it does, I believe it would be your graphics card causing the problems. You may be able to RMA or refund it after you find out it's bad; that would suck having to have it downclocked.
On the other hand, I've heard horror stories about that power supply, coming from Newegg. I know you can't base a product solely on their reviews, but DANG! 2/5 eggs... A few report their power supply going bad after 6 months or a little over a year. You haven't smelled any burning smells, have you? Another note though: my old Raidmax 450W PSU (came free with case
I know better now) that had 14A on the 12V rail could supply sufficient power to my 7800GT... for almost exactly 6 months. The PSU popped and sparked its way to its death one night, and I was afraid to put it back in. So just check those temps, and if they are below 70 or 80*C, your graphics card should be fine.
Good luck in resolving the issue. Sorry if none of this helps; just offering suggestions.