There's a sensor in the distributor, (hall effect) known to be the cause of a cranks but won't start problem. It tells the computer to fire the coil and continue to power the fuel pump. Not too expensive and easy to replace, just pull cap and rotor and get a short Philips screwdriver.

 

Thanks crazzywolfie ... I feel better ordering PCM with you having reached the same conclusion.

Good thought silvermopar, but I'm not so lucky. The hall effect sensor (aka ignition pickup) isn't getting its +8V voltage from the PCM. The sensor may be bad, but the PCM feed is definitely bad.

While waiting for PCM to show up, I am going to look into the trans overdrive solenoid. I stumbled on a Cardon* Protech sheet that says PCM/ECM failures are often caused by trans solenoids shorting out. PM me if you want the link.

Two of the 3 wires on this W150's trans solenoid go to the PCM. The third connects to +12V through the ignition. And this truck did have an electrical issue some years back where the wiring to the trans solenoid took out two of the fusible links.

I have no idea why those particular solenoids are prone to taking out PCMs, but I surely don't want to fry the replacement one.

 

Following up, my old 90 W150 sprang immediately back to life with a reman PCM.
Thank you crazzywolfie, silvermopar and HeyYou.
I really appreciate your help, and I hope to pay it back or forward somehow.

Overdrive solenoid had nothing to do with this PCM failing. It was just 27 years old and tired.
Reman on these 90s vintage PCMs is interesting. Apparently not a whole lot gets redone on these 90s vintage PCMs ...just three caps and possibly one or two diodes.
With decent electronic skills could DIY it in a pinch ... if reman or yard PCM aren't available.