I would like to share an experience that l might help someone with the same problem. To make it short, I did all the new plugs, wires, distributor cover, rotor. Needed anyway. No luck. And a lot of other stuff too. Finally, I checked voltages at distributor from ECU and found a lower than specified output from ECU. So I checked the same signal at the ECU connector. It was the same value: too low. I concluded I needed a new ECU. WRONG. I decided, since truck runs great in dry weather the there is a chance the ECU is getting wet in the rain. So I removed the ECU (something that I would normally try to avoid in as much as I am no mechanic). I put the ECU over an area heater with a fan for two hours. It was still raining. Then I installed the ECU, Plugged in the connectors and turned the key. VAROOM! She started! In the rain!

Now this is not a repair, but this might get you running rather quickly if you're in the same boat. I used a blow dryer, the kind used to dry hair. I mounted it as can be seen in the picture, on the opening on the ECU connected to the outside air duct. This is apparently designed to deliver cooling for the electronics in the ECU "clam shell" housing. I found when the same no-start condition occurs I can start the truck in 10 minutes. I happen to be driving a Ram which has an aux battery so I ordered a 12 volt Travel Hair Dryer so I can get hot air "on the road". I used it today, as it rained again with the same result. Even this low powered dryer got me started in 10 minutes. Hope this can help someone.
OK. I opened up the "clamshell" cover of the ECU shown in the pic above. Pic of the circuit board encapsulation are below. I used a small brush to coat the board (and fill the cracks with dialectic grease. Starts right off now in rainy weather every time!