Hey, I just got a EVGA gtx 550ti from newegg the other day and im having problems with it while im playing games. On battlefield 3 i was playing on Ultra settings at like 40fps but then 5 minutes into the gameplay i started locking up and everything started slowing down in the game. Also my gun was disappearing and reappearing. Ive lowered the clock speed to see if that was the case and it didnt fix anything. I also updated the drivers to the newest. I think right now its at 290. b4 it was at 288 and it was still happening. I also lowered the settings in the game and i still got the same problems.
My pc set up is:
AMD Phenom II X6 1090T 3.20ghz
I play at 19020x1080 res
Windows 7 64bit
Have you tried calling Evga tech support , there could be something wrong with the card and they could tell you right away if there could be a defect.
You could also try overclocking the cpu just a bit to see if it bottlenecking your video card. Try uninstalling the card and drivers and then reinstalling them.