Doesnt offer much in the way of help or reasons why,

... but you need a new TC ... according to the FSM ..


TORQUE CONVERTER STATOR CLUTCH INSPECTION.

(1) Insert Rotating Tool 7547 into converter hub and seat tool in one–way clutch (Fig. 31).
(2) Insert Stopper Tool 7548 in one converter hub notch and into outer race of rotating tool.
(3) Turn rotating tool clockwise. Converter clutch should rotate freely and smoothly. Less than 2.5 N·m(22 in. lbs.) of torque should be required to rotate clutch in clockwise direction.
(4) Turn rotating tool in counterclockwise direction.
Converter clutch should lock.
(5) Replace converter if clutch binds or will not
lock.