I have the exact same issue. When I pull on the tailgate with even a little pressure (guessing about 5lbs with 1 hand) and press the release button with the other, I hear the clicking, but nothing happens. I noticed it when I had some doors for the house in the bed and I had to unload the bed one door at a time lifting over the sides because it wouldn't open.
I took it to the dealer today, they checked for recalls and service bulletins, found nothing. The dealer said they tried it on another truck on the lot and it did the same thing. Now I'm wondering if I should take it in again.
How "normal" is this issue? Members that aren't having a problem, have you tried pulling on the tailgate while you press the release button?