Yep, that's a motor mount failure, from the sound of it.  You may need to replace the drivers side mount and add a chain to limit the travel of the motor.  I've had the DS mount get all buggered from really rompin' hard.  The stock mounts are good for insulating the vibration of the engine but they are flexible enough to allow the engine to sort of tweak itself up on the drivers side so that the mount is lodged on itself and stops the motor from returning to the stock position.