Why does my truck roll forward when put into park and engaging emergency brake?

This is Kevin with NWA Auto Shop. Without seeing the vehicle, I can only theorize. Based on the limited information given, these are my thoughts. There are several things that can cause this. Rolling forward in Park, lack of a parking brake and vibration in the rear end may or may not be related. There is no way to pinpoint a solution with only this much information. I would recommend taking it to a shop. Kevin