My GTX 970 is having drops of usage which causes severe FPS drops.

[douglas07luis]

In some recent games, after a few minutes playing with nearly 100% GPU usage, it drops for no reason to 45~50% for a minute or so, which then makes the FPS drop from steady 60 to 30 and below. I tried every possible configuration in-game, every single option on low and even with reduced resolution, it still happened.

This was happening once in Doom (2016) because my CPU and GPU were overheating. I got my computer dusted and the thermal paste reapplied. I then reinstalled windows and it went back to normal.

One month ago it started happening again with Shadow of War after some 30 minutes of gameplay. So I wiped my disk clean and installed Windows once again, just to find out the problem persisted not only in Shadow of War, but also in Destiny 2, which didn't have this issue before. Even in 2010 Mass Effect 2 the GPU was underperforming.

I checked the temps while playing, neither CPU or GPU went over 70ºC, which I know isn't ideal but it's the best I could get without a water cooler. Here in my country it is almost always 30ºC+, which doesn't help. And this was always the temperature I played with all these years, apart from when it was overheating.
I can't figure out what is causing this and I'd appreciate any help I can get.

 

[norcalsc]

please list all specs

 

[douglas07luis]

please list all specs

Mobo: Asus M5A97 LE R2.0
CPU: AMD Fx-8320, 3.5 GHz
GPU: GTX 970 GV-N970G1 GAMING-4GD from Gigabyte
RAM: 2 x 8GB DDR 4, 1600 MHz, I can't recall brand or model.
PSU: Thermaltake model SP-650AH2NCB 650W
HD: A 1,5 TB HDD which I also don't remeber the brand.