Vsync do that. Activating V-SYNC when framerate is under 60 it goes straigh to half, (30fps) ,so it is not a good option activating it if you are having FPS flutuation.
GPU = Graphics Processing Using = Graphics Card = Video Card. have you download latest driver version + catalyst control center? that helps a lot the framerate. maybe you had it installed before and now it is not correctly installed:http://support.amd.com/us/gpudownload/Pages/index.aspx