Had you tried mercon 5 fluid before going to the tractor stuff? I don't know what kind of a long term effect using the tractor fluid will have on the trans, but the merc 5 was specifically designed to eliminate shudder on these transmissions, so if it were my car, I would go with that.
Mike
PS. If the merc 5 doesn't solve the shudder, you would only need to replace the torque converter, not the whole trans.
Mike
PS. If the merc 5 doesn't solve the shudder, you would only need to replace the torque converter, not the whole trans.