[ImperialCrown]

With the PRND3L all lit, the TCM should store a 'no shifter signal' fault code. It doesn't know what gear has been selected and may go into 'limp-in'.
This can also be a communications bus problem as the TCM and MIC (mechanical instrument cluster) communicate information between themselves and the other modules over a 2-wire 'twisted-pair'.
The next time all the boxes are lit in the gear selector, 'thump' the top of the dash and see if the selector returns to normal with one box selected.
This might indicate cracked solder joints on the back of the instrument cluster circuit board that need to be reflowed. Usually the connector and larger 'through-hole' pin solder joints were susceptible to fracturing.

 

[ImperialCrown]

I don't know about a reset, but there is a self-test mode:

The instrument clusters are equipped with a self diagnostic test feature to help identify electronic problems. Prior to any test, perform the Self-Diagnostic Test. The self diagnostic system displays instrument cluster stored fault codes in the odometer display, sweeps the gauges to the calibration points, and bulb checks the warning indicators. When the key is in the ON position with the engine not running, the MIL will remain illuminated for regulatory purposes.

To activate the Self-Diagnostic program:
With the ignition switch in the OFF position, depress the TRIP ODOMETER RESET button.
Continue to hold the TRIP ODOMETER RESET button until Sof and a number (software version number (i.e. Sof 3.2) appears in the odometer window (about five seconds), roll the ignition key to ON then release the button. If a fault code is present, the cluster will display it in the odometer display. When all fault codes have been displayed, the cluster will display “end” in the odometer display. Refer to the INSTRUMENT CLUSTER DTC'S table to determine what each trouble code means.

100.0 LOOP-BACK FAILURE
100.1 ABS COMMUNICATION FAULT
100.2 BCM COMMUNICATION FAULT
100.3 EATX COMMUNICATION FAULT
100.4 FCM COMMUNICATION FAULT
100.5 ORC COMMUNICATION FAULT
100.6 SBEC/DEC/MCM COMMUNICATION FAULT
200.0 AIRBAG LED SHORT
200.1 AIRBAG LED OPEN
200.2 ABS LED SHORT
200.3 ABS LED OPEN
200.6 EL INVERTER TIME-OUT
200.7 EATX MISMATCH


CALIBRATION TEST
The CLUSTER CALIBRATION table contains the proper calibration points for each gauge. If the gauge pointers are not calibrated, a problem exists in the cluster. If any gauge is out of calibration, replace the cluster.

CLUSTER CALIBRATION SPEEDOMETER CALIBRATION POINT
1 0 MPH (0 KM/H)
2 20 MPH (40 KM/H)
3 60 MPH (100 KM/H)
4 100 MPH (160 KM/H)
TACHOMETER
1 0 RPM
2 1000 RPM
3 3000 RPM
4 6000 RPM
FUEL GAUGE
1 EMPTY
2 1/4 FILLED
3 1/2 FILLED
4 FULL
TEMPERATURE GAUGE
1 COLD
2 1/4
3 3/4
4 HOT


ODOMETER SEGMENT TEST
If a segment in the odometer does not illuminate normally, a problem exists in the display.

ELECTRONIC TRANSMISSION RANGE INDICATOR SEGMENT TEST
If a segment in the transmission range indicator does not illuminate normally, a problem exists in the display.