1998 GMC Sierra 2500 5.7 Vortec won't start when it's raining.

My truck has a tendency to not want to start when it is raining or there is high humidity. It cranks but will not fire. I have tried replacing the coil, plug wires, distributor cap and still nothing. I have no spark.

have you checked the crank sensor? on that year, that engine uses a crank sensor, and a cam sensor. the cam sensor is in the distributor. the crank sensor i believe is at the front and bottom of the engine.