Did u hook up a gauge to the reverse port on the tranny to see what kind of pressure u have? Could be a broken or wrong spring in the valve body. Or the valve sticking. Or the torque converter pressure regulator valve sticking not letting the pressure build up. One other scenario I had back in the 80s was the inner lip seal leaking when warm. I pulled the tranny twice and couldn’t see anything wrong. I had the front drum apart both times. Seals looked good. Second time I replaced them. I found a small pin hole in the inner seal after I removed it. New seals and problem solved. Kim
