The rear hatch seem to be jammed or stuck it wont
Crawl thru the front to the rear of the truck, Remove the two screws on the gate release handle (they are underneath the handle, two philips).
Gently pull on the plastic panel by the release handle, it will come out about 4 inches, it should be enough if you have a small arm (which I have.) I wedged a plastic 20oz bottle between the rear gate and the inner plastic panel, to keep the plastic held out, don't over stress the plastic it will break if its old enough, look down from the window hatch about 5 inches or so and notice the 2" x 3" opening, there is a lever in there that is moved by the actuator, and a piece of plastic (which is what my friends truck needs, if someone has a part number or aftermarket please advise) but if you reach in to that access panel, there is a slide that moves from right (looking at the gate from the inside) to left, moving it to the left (Opens the window)
Apon opening the window, remove the plastic bottle, and open the rear gate hatch, when the hatch is open there are two screws one on the left side of the gate, and on the right side.I hope this helps you out, remember: don't overstress the plastic, strip out the screws, or break the window..
Once you have everything out, you can replace the actuator or fix the wire leads that may have come loose form the rear door actuator keep you from opening the rear window.
Good luck and thank you for using fixya