[ImperialCrown]

The PCM test is performed by making sure that all of its inputs: power, grounds and sensor/switch signals are present and that it's outputs to the relays, coil, injectors, etc are working. PCMs are usually the 'last house on the block' when testing for a 'no start' condition. Everything else, including wiring and connectors has to be ruled out first.
The coil and injectors are powered up (+) at 'key-on' and the PCM controls the ground (-) sides of them for both spark and fuel to the right cylinder at the right time.
A good OBD II code reader/scan tool should be able to tell you if the PCM is seeing these cam and crank signals.
If you lost gauges but the van still ran OK, then that may be a separate problem (like broken cluster solder joints or communications bus issues)? Has a 'no bus' message ever appeared in the odometer?
An 'Authorized Software Update' sticker is still your old PCM with new software: 80bbcfda.gif
Someone may have flashed it to try and remedy a problem. Possibly this current one? Reprogramming a PCM would probably not fix a 'no-start' issue.
The correct PCM part number for yours is 56040325AD for Federal emissions and 56040326AD for California emissions. Remanufactured PCMs would be R6040325AD and R6040326AD respectively.
P1492 is a battery temperature sensor (voltage high) code, and would not keep the engine from starting. The sensor itself may be broken or disconnected.

 

[ImperialCrown]

Everything will have (+) power to it, the PCM controls and turns things like the coil and injectors on or off by providing the ground for them.
See if you can rent or borrow a scan tool. Go under the menu for the sensor display and see if the PCM is able to see the crank and cam signal.
If the tool cannot communicate with the PCM, the PCM may be in protection due to a short to ground in the sensor 5 volt supply circuit. This will prevent starting until the short is lifted and the key cycled off-on. Use OEM parts for replacement.

 

[ImperialCrown]

If you have the 5 volts at the sensors, then your 5 volt supply sounds fine.
The negative side of the coil and injectors should change while cranking, but the change may be too fast for a digital meter to accurately display. The numbers will just jump around somewhere between 0 and 12 volts. It should never stay steady while cranking.
If you see and smell damage to the PCM, I would start looking for a replacement one.

 

[ImperialCrown]

You need to do a PCM connector pinout voltage check. It sounds like you have 12 volts or ground on a pin where it shouldn't be. Probably when the ignition key is on for 12 volts. Do this with the PCM unplugged and with a test light.
You will want an engine compartment wiring diagram to trace wire colors. Has any wiring modifications or repairs been done?

 

[ImperialCrown]

I Googled and found nothing. Maybe a local main public library? Factory service manuals are factory copyrighted, so they are taken down soon after they are posted on the internet.
Other Dodge and Jeep trucks with this SBEC III(?) controller may have a similar pinout and wire colors.