I had the worst toughest vibration in all GM history. However, it only vibrated on accel and in park,,thus, bad engine (crank). It was easy for me to diagnose. LOL!!!! Just kidding, 4 mechanics couldnt figure it out before Vile did. Therefore, i'd be checking that rear end. Rumor has it, Vile knows a thing or two about these old chevy trucks.