Are you also using the factory round tube hitch?

If so, take this opportunity to do two things.
Upgrade to a heavy duty hitch. The round tube hitch is junk, even with it's weight ratings. Many of the GM truck sites call it the Flexi-flyer.
IF you upgrade the hitch, you will get rid of that very low hanging trailer wire connector, which is also a weak point. The wires behind it are too kinked on the factory install and exposed as well to road hazards, and they corrode and break. That's where your issue lies, I'll almost guarantee it.
Upgrade to something like this:
Hopkins Endurance 7-Way Trailer Connector Socket - Vehicle End - Ergonomic Design Hopkins Wiring HM48480
And install it to the left of your license plate; right in the bumper itself.

I did all of this on my 2002 Chevrolet and it worked out very well. All of that input is recollection from one of the GM sites I frequented back when I owned one.