Just to be clear, have you let the GPU cool down? Have you check overclocking settings? The most likely issue is due to memory overclocking. Make sure your memory is running @ stock speeds (sometimes your memory speeds can get stuck, verify them with GPU-z). Turn off "Apply overclock @ startup" and test. The next most likely cause is overheating. If the issues goes away when the GPU cools down you'll know but it sort of doesn't sound like heat. Lastly, sometimes the thermal paste applied from the factory gets dry and needs to be replaced. Easy fix, but it can be intimidating to anyone that hasn't cracked open a GPU before. Just be sure to use something like Kryonaut that isn't electrically conductive.
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Xeon E5-1680 V2 (IVY-E) Inside