GM-GMC: truck wont start when it rains, spray water, distributor cap

Question
We have a Chevy 1 ton dually that wont start when it rains, we have changed the distributor, and a sensor that was showing bad when we put it on the computer.No one seems to be able to give us an answer. Doe you have any suggestions as to what the problem may be?  

Answer
Most of the time when a vehicle will not start under humid or wet conditions it is related to secondary arcing, Old spark plugs,spark plug wires, bad distributor cap/rotor or coil. On a dry day spray water lightly on the engine while it is running and look for arcing on plugs wires coil and distributor. Good luck,hope this helps.