CS:GO Running well after a fresh win install, but performance tanking right after.

[kriptcs]

Hey everyone! So recently I've been having issues with CS running really poorly on my computer. I would get about 390-400fps in the fps benchmark which is worse than other systems. In game I would get about 300 fps but with drops to as low as 190 sometimes. That wouldn't be a problem if I didn't have a 240hz monitor and I would heavily feel the fps drops, buut yeah..
The kicker is that I would get proper performance (550-600fps) when I would freshly reinstall windows and run the benchmark with nothing on it, at most some out-dated nvidia drivers. As soon as I would start updating the drivers that's when my fps would go back to bad.
For context I tried all sorts of things, even modifying things in the bios to try to OC stuff but I reset absolutely everything back to stock and reinstalled windows, and these were the results.
My PC is working just fine outside of cs. With my general performance benchmarks doing well-ish (PC Specs also available with that link)
Also worth nothing that my CPU is stock running at 1.5V  (That's the CPU Core Voltage that is being displayed in the bios, between 1.42 to as high as 1.5) I tried undervolting it but it didn't really work properly and also had not changed anything anywhere.
I am quite clueless as to why this is and I would love some help on the matter, thank you!