Apologies if this is not actually a hardware issue. I believe it is, but I am not an expert, so I may be mistaken.

I use my PC mainly for gaming. On October 14th, everything was working fine. Games like DESTINY 2, Borderlands 3, and Code Vein were all running consistently at over 60 frames per second (Usually closer to the 70-80 range) on High or Max settings.
On October 15th, SUDDENLY all these games have inconsistent framerates, lower overall framerates, and significant stuttering when moving the camera/player character, or during combat. Borderlands 3, for example, now sees 30-50 frames per second during combat, in addition to the stutters when moving the camera. On the lowest settings, the framerate is better but still not as high as it used to be, sitting closer to 50-60 frames, and the stuttering is just as noticeable. Other games have the same problem, just to varying degrees. I did not install any new software or make any changes between the 14th and 15th.

So far, I have TRIED:
-Clean booting
-Updating video drivers
-Fully removing and re-installing video drivers with Guru3D
-Defragging the hard drive
-Replacing the HDD with an SSD
-Fresh install of Windows 10
-Removing and REARRANGING the RAM sticks
-Upgrading the graphics card from a GTX 1080 Ti to an RTX 2080 Ti (was already planning on doing this before the issues arose, so figured I'd give it a shot)

At this point, I'm guessing there's an issue with the CPU or Motherboard, but again, not an expert, so I'm not sure.

Specs:
Motherboard: Gigabyte GA-Z170X-Gaming 5
Processor: Intel i7-6700k
OS: Windows 10 64-bit
RAM: 32 GB
Graphics cards: EVGA Nvidia GTX 1080-Ti and EVGA Nvidia RTX 2080-Ti
Power Supply: Corsair RM850x

Task Manager, Afterburner, and CPU-Z while Borderlands 3 is running: