It has 80000 miles on it. Was driving in the rain today and went about 30 miles one way. Right before I got to where I was going the motor started missing. Felt like just one cylinder.

After 30 minutes in the store, came back out and started fine. Drove home in rain with no problems or missing.

Do you think this is a start of a problem or just shorted out in the rain? Either way it's not good and I'd like to find it so it doesn't happen again.

 

It sounds like water was causing the misfire. Make sure your spark plug wires are on snug at the plug and coil pack. Get a spray bottle full of water, adjust it to a mist, get out there after dark and spray where the spark plug wires go on the coil pack and watch for sparks.
Spray along the length of each wire, and at the boot. A great amount of heat builds up under the hood of these trucks, thanks to the EPA insisting that they be run so hot for emissions purposes, sometimes the wires deteriorate and it isn't visually obvious.
If your truck is the coil on plug setup- same thing, get things moist and watch for sparks to fly.