Cheaper/easier would be to swap in a new automatic or have it rebuilt. Will it not shift whatsoever now? It sounds odd that it would just fail like that with no slipping or warning. How many miles? Ever had it serviced?
-2002 Mustang V6: Eaton M112, E-85. 270/270 on 7psi
-1969 Chevelle SS396: 502H.O., TH400. Original L78 car, built 6/6/69
-Upcoming: 2015 Ecoboost C.O. performance pack