1997 80 series, all stock, 144k not abused and fairly well maintained. Tranny is shaking off the line (almost like torque converter shutter but more violent) and shuttering on downshifts before it finds its gear and goes. Does this about 50% of the time, 50% no symptoms. Hate to swap the tranny before I am sure its shot. Just did fluid and filter with no change. Any direction with this A343F would be appreciated. thanks!