Two different trucks and two different travel trailers. Same issue. I’ve been trained by General Motors on proper hitch/trailer loading and towing procedures. Hitch and brake settings are dialed. Hitch is a Reese dual cam with 1200 lb bars. Same set up that my RV tech friend has sold and setup for years again without an issue like this. 🤷🏻♂️Looking at your pics, it almost appears as if the pin is wearing excessively or getting ready to shear.
Have you checked your trailer brakes and their settings? Do you feel the trailer brakes "grab" like the drums might be warped or something? The only other thing I can think of is to check the hitch to see that it is binding itself in the tube and not sitting on the pin. I.E. check to see that there is no gap on the top (IIRC the hitch gets pulled to the top of the receiver to lift the rear of the truck).
What model of WD hitch do you have? I want to look through the instructions. My Blue Ox said to set trailer and truck on level surface, take two measurements: 1 - unloaded hitch height, 2 - loaded hitch height. The difference should be about 1". I had to play with the settings on the chains a couple of times to get it where it needed to be along with keeping proper traction. About 1-1/2" was the magic number for me. Truck sat level, and had good traction. If it got to less than 1", I would loose rear traction on dry ground. Stock tuning on 06 true LBZ.