I have left everything at stock speeds. I have not OC anything. I do have an application that specifically allows me to OC and monitor my graphics card and another one specific to everything else.(these applications are why I know its not an over heating issue) and as i have said i have left everything at default.
You said the PSU might be the issue? Is it because it doesn't provide enough power? can you clarify.
Note- haven't experimented with OC my system.
A faulty PSU will fail when put under load (like when the CPU and GPU are maxing out during gaming). A quality PSU like those by Seasonic are worth their weight in gold, so to speak.