I've posted this to Reddit, and the Steam discussions of PA, but I should ask it here too.
So I installed the game after a long while, and I was surprised by how laggy it was. I pressed alt+tab to switch to my 2nd screen to check for fixes, and the lag was gone.
So when the mouse is on the 2nd monitor (on chrome or something, like right now), I can see the game running very smoothly. But when I switch my mouse to my primary monitor, and click somewhere on the game, it starts lagging again heavily.
What gives? Any known fixes to this? It hurts to be unable to play the game, when I know my PC can very well handle it.
This question has received the maximum number of answers.