We'll need more information than this to diagnose why a CPU might be underperforming. A full list of system specs would be great if you could post them. Also, how are your temperatures looking?
HWMonitor from CPUID is a good utility for monitoring all of your hardware and will also show you the temperatures of most of your components:http://www.cpuid.com/hwmonitor.php
Particularly high temperatures cause what is known as throttling; where a CPU will slow itself down in an attempt to cool itself to safe temperatures when it is overheating. This could be what you are seeing here.
Post back with your temperatures and any other information might be useful and we'll go from there. Good luck!