The only fighters with dive brakes in AH are the P-47D-25, P-47D-30, and P-38L.
At high speeds it was normal for controls to stiffen. This is because of the pressure of the airflow over control surfaces. At very high speeds there is also a shock wave phenomenon called "compressibility" which causes reduced control response.
If you have this problem in a dive you should cut your throttle and use pitch trim (k key) to give yourself a good chance to pull out.
You can avoid this problem altogether by reducing your power before diving.