GMC Repair: electrical problems, crankshaft position sensor, mechanic check

Question
Dear Sir:  I own a 2000 GMC Sierra 1500 with a 4.3 L V6 basic half ton truck. My problem is that if I park my truck overnight and it has rained or is very humid overnight, the truck won't start in the morning. I have confirmed that it is not getting any spark to the plugs and have replaced the distributor cap and all looks well inside of it. If I plug in the block heater for an hour and a half, it will warm up the engine enough for it to start. Is there a sensor that is humidity sensitive to the point where it will prevent my vehicle from starting? My mechanic knows of five other trucks that have the same problem and no one knows of a solution. Can you please help.    Thank you     Bruce Smith

Answer
Hi
I would HIGHLY suspect the Coil wire. I have run into the NUMEROUS times. Quick fix would be to remove the loom on the wire now, and TAPE the entire length with black electrical tape.
If this is not it, have mechanic check for RPM's on his scan tool.
If not, suspect the CKP (Crankshaft Position Sensor).
THere are not many items to create a no spark condition.
I Hope this helps.
Good Luck
Pawl