It's a 5.9, not a 5.7? That changes everything they are completely different ignition system, your distributer probably has lost its seal and is letting moisture in. Change your cap rotor and wires you'll be good to go.

And for the record early 5.7 had one plug wire going from the coil to a secondary plug on another cylinder. In 2006 they changed so that both plugs were fired by the same coil and lost the spark plugs wires.