Instantiation and Deletion very slow... HELP..

So I am making a game, which you can go on forever, like minecraft but 2d, and im going to use cubes. But the issue with this, is that for some reason if I am running on an update function, I am only able to generate about 30 blocks a second, when my framerate is upwords of 300... This is the same for Delete(gameobject)... Please help - Max