For various reasons, some CPUs can start throttling and will end up running at a fraction of their rated speed. This can be heat related but it can also be power related. Have you tried running ThrottleStop?
ThrottleStop 8.00 beta 4
https://drive.google.com/open?id=0B0dpSo9k93jDNXlJVzdsSHh6a3cCheck off the Log File option, go play a game for a while (15 minutes), exit the game and then exit ThrottleStop. Have a look in the ThrottleStop folder for a sub folder called Logs and then look in that folder for the log file. Open it up and copy and paste the data to
www.pastebin.com and then post a link here so I can have a look. It would be best to turn on GPU monitoring in the ThrottleStop Options window before you start logging so your GPU temperture is included in the log file.
This program has fixed a lot of under performing laptops. When you are having problems like this, it is either the CPU or the GPU or sometimes CPU throttling can cause the GPU to slow down. When finished testing the CPU, try using GPU-Z to log performance information about the GPU when gaming.
In ThrottleStop, make sure BD PROCHOT is disabled. Don't let the 101 features scare you off. Just learning about a handful of options can make a big difference.