I wired an incandescent bulb into the rear of the truck, one on each side of the truck.
Did a 200 mile drive across state, drove well but no change in behavior.
When I got back I check the function of the third brake light on the top of the cab. It illuminates when my doors open but not when I hit the brake pedal.
Inside my junction box at the rear of the truck where all my tail light connections are made is a rogue black wire that isnt hooked up to anything. I have never known what this is but maybe that is the wire for the third brake light? I had assumed the connection for that would have been way back at the fuse panel instead of going to the rear of the truck, but maybe I am wrong.