GT Newbie

Hi- forgive my ignorance, but when I mash it to the floor in my automatic and it shifts gears at around 6000 R.P.M. is this because that's the way it was designed (still at perfectly safe revs), or is it then bouncing off the rev limiter?
I would think that the limiter was more for a manual tranny which would be much easier to abuse by choosing to keep it in gear too long- but I'd like to be sure I'm not "beating" it by almost putting my foot through the floor and keeping it there too long (only got about 550 miles on her so far).......
thanks!