1993 Plymouth Voyager slipping

Everything is controlled by the PCM. You should be getting fault codes. Have the PCM read to see if there are any codes stored?

DESCRIPTION & OPERATION
TORQUE CONVERTER CLUTCH LOCK-UP
30TH & 31TH
Torque converter clutch lock-up is activated only in Drive and is controlled by Powertrain Control Module (PCM). See PCM LOCATION table for mounting location. The Torque Converter Clutch (TCC) solenoid, located on the valve body, receives battery voltage when ignition is turned on.
NOTE:The TCC solenoid may be referred to as the lock-up solenoid, lock/unlock solenoid or Electronic Modulated Converter Clutch (EMCC) solenoid.

The PCM controls the TCC solenoid ground circuit for torque converter clutch lock-up operation. Torque converter clutch lock-up depends on input signals to the PCM provided by input signals from various sensors.
Torque converter clutch lock-up is monitored by the PCM. The PCM self-diagnostic system stores a diagnostic trouble code in the memory in event of a malfunction. Diagnostic trouble code can be retrieved for torque converter clutch lock-up diagnosis. For more information on self-diagnostic system, see SELF-DIAGNOSTIC SYSTEM in this article.

TORQUE CONVERTER CLUTCH LOCK-UP SYMPTOM DIAGNOSIS
NOTE:The following are possible causes for designated problem. Some possible causes may not apply to all applications.

Loud Chatter During Torque Converter Clutch Lock-Up When Cold
Defective torque converter clutch
Faulty torque converter
Leaking turbine hub seal
No Torque Converter Clutch Lock-Up
Defective TCC relay or wiring connections
Defective TCC solenoid or wiring connections
Failed torque converter clutch
Faulty input shaft or seal ring
Faulty oil pump
Faulty torque converter
Leaking turbine hub seal
Sticking governor valve
Stuck converter clutch valve
Stuck switch valve
Valve body malfunction
Shudder After Torque Converter Clutch Lock-Up
Defective torque converter clutch
Faulty oil pump
Faulty torque converter
Improper engine performance
Improperly adjusted throttle valve cable or linkage
Restricted oil cooler
Valve body malfunction
Torque Converter Clutch Locks Up Or Drags In Low Or 2ND Gear
Faulty oil pump
Stuck switch valve
Valve body malfunction
Torque Converter Clutch Stays Engaged At Low Speeds In Drive
Defective TCC relay
Sticking governor valve
Stuck converter clutch valve
Stuck switch valve
Stuck TCC solenoid
Valve body malfunction
Torque Converter Clutch Will Not Disengage
Shorted wiring or electrical components
Sticking governor valve
Stuck converter clutch valve
Stuck switch valve
Valve body malfunction
Vibration After Torque Converter Clutch Lock-Up
Faulty torque converter
Improper engine performance
Improperly adjusted throttle valve cable or linkage
Vibration Or Shudder During Torque Converter Clutch Lock-Up
Faulty oil pump
Faulty torque converter
Improper engine performance
Valve body malfunction

Once you have codes repost for description of fault?

MIL Diagnostic Mode
Start engine (if possible). Move transmission shift lever through all positions, ending in Park. Turn A/C on, then off (if equipped).
Turn engine off. Without starting engine again, turn ignition on, off, on, off and on within 5 seconds. Record 2-digit fault codes as displayed by flashing MIL.
For example, fault code 23 is displayed as flash, flash, 4-second pause, flash, flash, flash. After a slightly longer pause, other codes stored are displayed in numerical order. When MIL begins to flash fault codes, it cannot be stopped. Start over if count is lost. Code 55 indicates end of fault code display.
Refer to FAULT CODES/MESSAGES to translate trouble code number to a DRB-II fault message. Once trouble area is identified, refer to TEST FC-1A. Use DRB-II fault messages to find appropriate test.
As an example, a 2.5L engine starts and runs but has a driveability problem. MIL indicates a Code 14. Refer to FAULT CODES/MESSAGES to translate trouble code number to a DRB-II fault message. When DRB-II fault message is obtained, refer to appropriate test. To clear fault codes, see CLEARING FAULTS.