I sent the pics to my brother, who has worked in dealerships for 15+ years and he said that one dealership he worked for pre-wired all their cars for tracking/kill switch devices for high risk (bad credit) customers. In some cases, banks require them in order to finance the car to a high risk customer. He said that's what it looked like to him. Makes sense that it would have to be somewhat hidden and not easy to unplug or disable.
The dealer I bought it from traded it with another dealer from Houston because it matched my desired specs better than what was in their local inventory. I'm guessing maybe that dealer sticks the harness in when they prep the trucks. Or maybe someone else was trying to buy the truck before I did, so they put in the harness but then removed the device...