Formally called the Chevrolet C/K, C/K is a series of trucks manufactured by General Motors and marketed under the Chevrolet and GMC brands. The C/K line includes pickup trucks, medium-duty, and heavy trucks.
Have you checked to see that the wires that go between your door and it frame of the truck are frayed or worn from the years of opening and closing. My 98 Chevy 1500 had the exact same problem inside of the plastic tube that houses the wires. Just a thought :)