I did everything right, also finished Gorgrond (as Horde not Alliance) and now I'm 58.
I think I didn't finish Grogrond actually, I had a couple quests that recruit a follower, Kaz the Shrieker and the Iron Approach scenario that takes you to the Iron Docks. With those ones I dinged to level 60.
I think the dude said in one of his videos or reddit posts that you'll end up doing a couple more stuff in Talador as well if you don't hit 60 in Gorgrond.
Level 50 though after finishing Gorgrond? You must've done something wrong.