Probably, the CPU does not use the maximum possible frequency because it does not need it.
If your GPU is relatively weaker than your CPU then your GPU will work at maximum and your CPU will run relaxed.
You can use a program like MSI Afterburner to verify your CPU and GPU load simultaneously.
So that people can help you better it would be convenient to give the specifications of your PC (gpu, monitor resolution ...).
Additionally you can use the "Intel Processor Diagnostic Tool" to check the limits of your CPU.