I'm assuming the truck runs fine otherwise.
It sure seems like a high voltage electrical problem to me. I'd exhaust all the possibilities there first, before going on the fuel system. Sometime you have to completely remove the coil, put it on a table, and clean it off with soap and water before you can see a crack. The crack can be so tiny it is almost impossible to see. I had a similar problem with a VW Rabbit years ago, and I sprayed water all over the engine, and it would run fine. The first time it rained, it would stall. When I removed the coil I found the crack.
Have you check for carbon tracks on the inside or outside of the distributor cap?
Does the ignition system use a separate condensor? That's a possiblity too. You might try replacing it.
If your car has a capacitive discharge ignition system, that could be the problem. Those don't take well to dampness. Usually you have to replace the whole module.
If the problem is in the fuel system, my first guess wouldn't be the main injectors. You can listen to them as posted above, but I doubt doing so will tell you much. My first guess in the fuel-system would be the cold-start injector. It is supposed to inject some extra gas if the engine coolant is below a certain temperatrue (usually around 90-100 deg). Perhaps something is failing and it isn't doing it's thing, which would make the engine hard to start in colder temperatures. Add dampness to that, and it might indeed not start at all.
Best of luck.