Ford tranny problem: revised?

Ok....have some proper terms....The transmission will not downshift when there is a drop in governor pressure (when slowing down) It stays at whatever gear I am in until I am almost at a stop. The transmission is not acknowledging the fact that I am slowing down or coming over a hill until I am almost at a stop. How can I correct this problem? 1990 Ford E150 Club Wagon 5.0L either c6 tranny or AOD (shift column shows PRND1 only).