Don't know if this will help but when I was playing Grim Dawn a while back I started noticing slowdown/lag occurring more frequently, to the point the game would crash.
I finally decided to clean out everything....My gfx card is almost completely enclosed in plastic. I had to open up the entire thing. Must of had 25-30 screws to undo. Inside were mounds of dust which basically meant the fan wasn't circulating any air across the card. Once I cleaned all that out everything was fine