At what resolution are you playing at and what size monitor? If you are playing on lower resolutions that will put more "pressure" on the CPU. You can think of it like a sliding scale. The lower the resolution the more work load is put on the CPU. The higher the resolution the more work is put on the video card.
A few other things to check into:
Windows Task Manager> Applications- Do you have anything running?
Go into MSConfig and look at the services tab. Click at the bottom where it says "hide all MS services" This will hide all the important stuff an leave you with the junk running in the background. Cancel all unnecessary programs.
Also I would do a virus and Malware scan with Avast and Malwarebytes.