What is the temperature of your CPU and GPU?
Both idle at around 35 and come up to 70 when under stress.
I had a heat issue before, it went up to 100 but it didn't cause lag like this, only when it needed to cool down which was for a few seconds.
I can hear my GPU not work, as in the fans.
Usually when i run the game on ultra they speed up a bit and fps is steady
When what i said happens they just remain as they are, quiet, and its very heavy lag.