Like I said above, while playing some games I can run fine for awhile, then for no reason I get a huge drop in fps. I run an i5 6500 and GTX970 with 8gb ram.

Compared games, thinking it was the game I was playing, but no. It was definitely my rig.

It does go back to normal eventually, seemingly after I unplug it for awhile. Sometimes I can play a game for a couple of hours before experiencing the problem, sometimes minutes, once I went a week without problems.

Funny enough, I checked the Windows Experience index deal the first time I had problems, and my processor score dropped to a 4.5 from it's standard 6.8. After disabling a lot of start up programs and all that, my score actually bounced up to a 7.6 and has held despite the issue reoccurring. I even checked system logs to find any messages about why it changed, but nothing.

So to diagnose the problem, I downloaded MSI afterburner to check my stats. Power was fine, gpu was running well, temp for both cpu and gpu were great (avg mid 30°s for cpu and up to about 60° for gpu), but cpu use would be like 70-100 for all 4 cores on a game (Grim Dawn) that my rig has historically run at max settings at around 100fps in combat (with issues I get 10-20 fps now).

2nd round of diagnostics, I downloaded User Benchmark to further test performance. I ran it first right after I started having performance issues that session, and it showed that my processor was actually a potato, but everything else was pretty good. Later, I ran it again when everything was running fine and it reported that my processor was running fine. Did it a 3rd time while having issues, and yep... potato again.

Basically, I have no damn clue what's going on, or why the issue happens so randomly. I don't want to take it to a repair shop if I'm just going to have to buy a new processor anyway.

Any advice would be super helpful, I'll try to keep an eye out so I can respond to any follow up questions you might have.

Edit: I've had my PC for about 9 months now, and this is the first I've had this problem.