You may have issues with your card. Pixelating often occurs when the GPU memory is failing. I just learnt that in some cases this can be due to solder cracking on the card. Apparently you can "bake" the card in a manner that remelts the solder. Apparently the process known as GPU Baking can be found on Google. This is of course is assuming the card is the problem at a hardware level for that reason. Make sure your PSU is putting out good stable voltage as this can affect GPU behaviour.