The problem might be temperatures, even if your cpu and gpu tems seem fine there could be other things that could be overheating like VRMs and memory, make sure that nothing in the PC is overheating and if thats not the issue try downcloking parts of your PC (i recommend RAM then GPU then CPU) because PC parts degrade and overtime sometimes they need more voltage to operate at a certain clock speed, a solution to this is either to add voltage or to downclock the part.