|I would not have purchased that power supply, you have three 12 volt rails which is not ideal for running high draw components like your video card. Your individual specs are:|
+3.3V@25A, +5V@25A, +12V1@22A, +12V2@22A, +12V3@25A, -12V@0.5A, +5VSB@2.5A
Since your 12Volt amperage is divided among three rails, you may not be able to access all of your available amperage for your video card and while gaming your video card is drawing much more amperage than for normal computing. I would lean towards the problem being with your power supply not being adequate for you needs. If you can purchase a new power supply under the condition that if it does not solve your problem, you can return it for a refund, and find it locally to save you the postage, then I would definitely try that. Look for a power supply with a single 12Volt rail, 80% certified efficiency or better, active PFC, and a quality name brand.
These are very good choices:
+3.3V@22A, +5V@22A, +12V@54A, -12V@0.3A, +5VSB@3.0A
+3.3V@30A, +5V@30A, +12V@62A, -12V@0.8A, +5VSB@3.0A
You have to be a little bit crazy to keep you from going insane.