I have NH-D15 cooler and temps never go beyond 60C while gaming.how is the temp? It is possible that the chip is beginning to degrade.
I have Corsair Vengeance RAM 16GB (2x8GB) 3000MHz running at that advertised speed using XMP.let's try keeping the CPU clock at 4.7Ghz same voltage but run the ram at default clock and see if the problem still persists.