So I tried doing everything you suggested, and the issue is still there. I was even able to upgrade from Windows 8.1 to Windows 10 in that time, and I've still got issues. I took a short video using my phone to show how severe the problem is. Maybe this could give you an idea of what it might be.

I am not, I have checked through Task Manager and the 64bit version of Arma is running at all times. From what I have seen from searching for "3 fps bug," it usually involves someone running the 32bit version, or in one case that I saw, someone's CPU overheating. I think it's important to also mention that this issue drops the game WAY below a frame per second as I mentioned, it is quite literally a single frame every 5 seconds or worse.