Dude Id be soo freakin pissed, that would be covered im sure by my dealer I know for a fact they would never sell me or anyone I know a truck with a tailgate that bad especially on a 2011. that truck either got beat down the roads in the winter or somebody simply didn't care and just neglected their ride. regardless it needs to be addressed, if there is rust there god only knows what up under the bed, behind the taillights and all the seems welded throughout the truck. Id carefully inspect by pulling out the tails and looking up under your truck carefully, im sure there could be a lot more hiding.