93 4.3L misses when wet, static on radio

Chevy half ton, two wheel drive, 4.3L with the four speed. When it's raining, it misfires under load until it is driven about 15 minutes. I have also noticed static in the radio (aftermarket) that started in the last two weeks that seems to be related to engine speed and load. It also gets better when the truck has been driven for about 15 minutes. I have replaced the rotor, cap and ignition wires. The alternator was replaced about 2 weeks ago. I noticed tha static after that, but can't say for sure if the alternator has anything to do with it.

A new coil solved the problem completely.