Inexplicable Stuttering on PC

Ryzen 9 3900x GTX 1070 16GBs of ram Gears 5 installed on a Samsung 970 Evo plus. Windows 10, steam version.

So, up until yesterday I had no performance issues whatsoever, staying in the mid 80s fps range on all ultra settings. Suddenly, and for no reason that I can see, I've been getting stuttering (frame rate is still reported as mid 80s, but it looks like there are frame drops.) Making things even stranger, the problem seems to resolve itself after 10-15 minutes of playing, but will return every time to game is freshly launched.

Things I've tried so far:

Turned of windows 10 game mode Verified game cache on steam Uninstalled ultra textures Manually selected my GPU in the video menu Turned on/off async compute Generally played around with all video settings

My CPU is reporting as a comfortable 30% usage so it doesn't seem to be a cpu problem.

I'm at my wits end here. I have no idea what else I could try. Any suggestions would be very appreciated.