I originally downvoted because I lost my keys. That, and I thought you could have done a little more to narrow the problem. Perhaps confirm if there is any problem with the lowest settings and then work upwards. Just a glance at the question indicates you have the highest settings on for more settings and pretty much wondering what you can do to improve performance.
It seems like a no-brainer to suggest working upwards from the lowest settings to finding a point at which your machine runs the game smoothly. Hey, maybe you find the same problem on the lowest settings. There are third party plugins/tools etc that can check if your current machine is capable of running a game.
Anti-virus kicking off a scan mid-game always grinds your game to a halt. Not sure if you checked for that already.
Also, when people comment/ask why the downvote it tends to lead to more downvotes. I'm not saying that is my reason, just that it can be a reason for downvotes.
Anyway, I found my keys this morning so removed my downvote.