First check the fluid level, if fill its internal on high mileage transmissions
Excessive delay, slipping in reverse in 722.3 transmissions is cause by B3 clutch flaking, excessive clearance , B3 apply piston then over travels exposing the seals, when the return springs push the B3 piston to its static position the lip seal gets cut.




More reading

http://www.peachparts.com/shopforum/showthread.php?t=95670&highlight=Revrse

http://www.peachparts.com/shopforum/showthread.php?t=141596&highlight=Reverse



http://www.peachparts.com/shopforum/showthread.php?t=141596&highlight=Reverse