Help!! new here , vapor lock!

Help! my 93 chevy astro van vapor locks when driven a long way in the heat! I know it is for certain vapor lock, when it dies , i pull the gas cap, and there is so much pressure it nearly shoots the gas cap off. after the pressure goes down in about 5 min, it starts and runs fine. Right b4 it vapor locks , the fuel pump makes a whining sound. What is the cause of this, and what can i do to prevent the vapor lock?

Check the EVAP stystem. There is a tank pressure control valve in the EVAP system to limit pressure and vacuum. Restore the system to proper operation and the problem should be solved.