I was surprised that the AA agent at MIA tried to give me a hard time with it.... I mean, yes I understand that technically I was breaking the 2 carry on policy but its not that my 3rd item was a rollerboard or a large bulky item, these things fit perfectly in the crew closed and also in all overhead bins... but in the end I think this all comes down to interpretation and goodwill of each agent involved. I lucked out because there was a supervisor near that decided to overrule the agent.