Yes, the rear windows, auto headlights, and drl will have to be enabled by programming at the dealership. It cost me 560.00 to get done. These trucks can't get afm delete without a lot of work on the ecm. That cost me 590.00 where as my 13' PPV cost a hundred. They are great driving trucks. Parts are rich and sometimes hard to find in the boneyards. I had to get carpet $300, console,$200 w a driver seat 300. It's a great vehicle now. You are dealing with a 6 spd. Trans and they have a kind of funky failure rate.
Whether or not the rear windows, auto headlights and DRL work, or not, depends largely on the truck options, and how the department running that particular vehicle configured them. Our '18 came with working rear windows and doors and auto headlights, but no DRL. But yeah, enabling these options may require a trip to the dealer and handing over $$$!
Agreed, they're great vehicles. We replaced our '10 PPV with the '18 model. Because of the weight and how they're driven, I'd check the sway bar end links, front and back when you get the vehicle. The front ones on our '18 were blown out. Replacement is pretty easy, but something to look at. Additionally, if the vehicle originally had dual batteries and the upfitter removed the aux battery (front corner, driver's side), verify they did a good job and at least taped the ends of the cables they removed.
Ours has developed a leak on one of the oil. cooler lines where the hardline connects to the rubber hose. Replacing that is a bit more of a chore, and you may opt to just pull the cooling lines at the engine and install the factory block off plate.
