if it occurs in neutral it is not the torque converter. you have an output Driveline vibration more than likely that is the CV'S having excessive wear and you're feeling the balls hitting the end of the worn section to the un-worn section which creates a notchy type vibration that you typically see when you lower the car and put the travel of the CV bearings closer to the end of the wear
it basically removes the constant velocity portion of the CV joint because what you're feeling is small acceleration and deceleration rates that you typically see with a u joint
