Question Sudden FPS decrease/drop and micro stutter in most games

Feb 25, 2020
GTX 1060 3gb OC
Intel i5 2500 3,3 GHz
8 gb ddr3 ram
120gb SSD 1tb HDD
Coolermaster 650 W

Playing all of my CPU intensive games (source games like CSGO, Insurgency, gmod) and Company of heroes 2, I've suddenly, out of nowhere got an fps decrease from eg. (csgo dust 2 deathmatch) from 150-90 fps to 140-70 fps with this weird microstutter and jitter happening as well. Games feeling a lot choppier and harder to aim. Temps seem fine, ran virus checks, defraged, verified game cache, uninstalled GeForce Experience, updated GPU driver, nothing helped so far. Could the old i5 be biting the dust or is it a software issue?
Assuming your SSD is the OS and application drive, is there still enough empty/free space remaining? (Many recommend 15-20% of the drive's space be kept free), and 120 GB drives are often challenging for this reason)

You can try terminating all non-essential services/applications (turn off all cloud storage, AV, etc. for testing) to free up some CPU/RAM to see if that helps any. (8 GB of RAM is increasingly somewhat minimal for Windows 10 these days, if applicable)

You can confirm temps and clock speeds are fine with HWMonitor and CPU-Z/bench/stress CPU, respectively...; similarly, perhaps GPU-Z will let you know if anything abnormal is occurring / the GPU....

If there might be a botched driver or Windows update applied, and this just started recently, perhaps you can rollback to an earlier restore point? (If function and frame rates miraculously restored, it would seem to be OS/driver related)

If it is a glitch of some type, and no actual hardware failure, than perhaps a fresh quick format/reinstall will take care of it...