Framerate issues!

I have a High end PC and can run TF2, titanfall, and Battlefield 4 at high graphics at a high fps.
I used to have more then 150 FPS on max settings for gmod, then suddenly I just randomly started to lag.
I dropped to 30 FPS for no reason at ALL, and even when I lower my settings, my FPS stays the same.
Ive tryed uninstalling ALL MY ADD ONS, and uninstalling the game entirely, but even without any add ons and reinstalling the game, it still ran at 30 FPS and less.
I tryed seing if this happened on other games too, but I still ran at a good FPS.
Help please!

what’s your pc specs? anything you installed recently? also you didn’t happen to set fps_max to 30 and forget about it did you

How is your CPU?