3 years old now hitting the terrible twos

Our Connor has just recently hit the terrible twos, but he will be 3 on the

27th.  He is a good little boy, but always very curious.

He has started to become beligerant.  Examples:
Not stopping when someone tells him to (running away)
Not coming back when someone asks him to
Sassing, when he does say thank you sometimes it is not in the best tone
of 
voice
Hitting things (the cat, although I must admit she is a prickly thing and 
she is not as innocent as she lets on)

Any ideas?