Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Welcome Brad. There is a VEH stop fuse, A CHMSL fuse, and the left and right trailer fuse. If those are good, the you need to start by checking the junction block at the back of your truck in front of the bumper for a bad connection. I would test the light blue wire for power with the brake pedal pressed. If you have power to the junction block and none out then you need the junction block.
The connector and junction block is the common issue on these. Your reasoning for the brake light is accurate, the brake switch is working. Just so you know the rear lights have a separate wire from the front of the vehicle than the rv and trailer plugs. The RV lights have nothing to do with the rear junction block. your bumper to bumper warranty is expired. Also, I only mentioned the fuses as confirmation that you found them all.