Download HWMonitor, CPU-Z and maybe CoreTemp.
These programs will monitor cou usage, activity and temperatures.
Run anything demanding benchmark (game, intel burn in etc.) and monitor the above. Keep an eye on the temps in particular.
If at full load it only goes up to 3.4 Ghz, then there;s something wrong. I suspect you are manually adjusting the clock when it is not needed (i.e. increasing clocks when the CPU is idle.)
Hope this helps.