2005 Chevrolet Silverado 2500HD misfires in the rain

Ok so we have a 2005 Chevy Silverado 2500 HD 6.0 motor. Everytime it rains the truck throws a random misfire and won’t run right. Any suggestions anyone can give me? We have changed all coil packs,plugs wires, intake gaskets, checked fuel rail to make sure it wasn’t clogged. I’m at a lose and can’t figure this out now and neither can a Chevy dealer

Look for corroded ground connections. The ground strap from the engine, any grounds you can see in the engine compartment and any you see under the truck near the engine. Clean them all. Tighten them and coat with a little white grease. That might solve your problem.

I was going to suggest the same thing. Probably bad ground. I had the same truck and I’ve also experienced the same problem you had. My main ground was rusted and corroded so I ended up replacing it and I never had that rain issue again. Hope this helps

there is a ground underneath the battery tray, be sure to check that one too.