Still getting "Check trailer wiring" message 2014 Silverado

I posted this about 6 months ago, but didn't want to resurrect an old thread. My truck is a 2014 Silverado with factory ITBC brake controller built in. While towing, I randomly get the "Check trailer wiring" message on the dash and then a second later, it says "Trailer connected". During that split second, I indeed have no trailer brakes. Several months ago, I replaced the plug on the trailer end with the Pollack brand plug as that is what some here recommended. I was hoping that would fix the problem, but it did not. This weekend was my first time towing any distance since doing this and while towing it home today on a 4 hour drive it was doing this constantly, for 4 hours. Obviously, this was making me very nervous. Wiggling the plug and plugging it in better did not help the problem. I crawled under the trailer and found the end of the main trailer plug where it goes into a metal junction box. I opened the juction box and had my son sit in the truck with it running while I wiggled these wires in the junction box, and nothing happened. The only way I could recreate the message was to unplug the camper and then plug it back in. What should I check next? Could a short between this junction box and the actual brakes be causing this problem? Could it be a problem with the truck or the truck end of the plug? I'm hoping someone here can help. Thanks.