2002 S-10 4.3 won't start in wet weather

Besides changing plugs, plug wires and distributor cap, where do I look next to solve the problem of starting the truck in wet weather?

Are you saying you have changed the wires and distributor cap? BTW the coil is also moisture sensitive.

Spray those parts, and ignition wiring, with silicone. It’s can keep the moisture out, and the electricity in.