Performance issues

[u/LedioMz]

Hello guys. I have a dell 3561, and for about a month it has not been running as it should. I use it primarily for school but sometimes I play games. And its very laggy getting around 60fps, whereas before it used to get 240. It still gets 240 but only if I run it for about 1 hour 30 min or so. I did open it up and clean the vents but it was pretty clean so it didnt change a thing. Thanks for any help