WARNING: This page is about a different car, the 1994 Cadillac Fleetwood. However, it is still accessible from the selected car via links, so may be relevant.
Check all connections at the transmission. An open in ignition feed circuit can cause multiple codes to set.
Fig 1: Code 84 Schematic (Fleetwood) 3-2 Control Solenoid
Fig 2: Code 84 Flow Chart (Fleetwood) 3-2 Control Solenoid