Do you have a lot of rain where you are at? I was recently doing some work on my 2009 Silverado and had to remove several of the panels. We normally don't have much rain but this winter it has rained quite a lot, I pulled the threshold cover under the door and found that the rain had filled the space under the cover had refilled with water. If your truck has the same problem check for a break in the wiring as that could cause a short and the water will short to the chassis.