You would have two items failing.
One the cone clutch on the direct clutch is not holding. Could be the clutch lining is shot, springs engange the clutch into direct, or the overdrive pistons are not releasing causing the clutch not to engage. Overdrive is engaged by applying hydraulic pressure to the overdrive pistons and the solenoid directs the oil to the overdrive pistons.
The Gearvendor unit is in direct due to spring pressure when no power is applied to the solenoid.
The other problem is regardless of the clutch the sprague or one way bearing will allow for forward movement, but not reverse.
It could be the solenoid hanging up not allowing the overdrive pistons to release, but the one way bearing means it will need to be pulled out and replaced.