My child is younger version of Loy58's. They are so similar! I don't have much advice for you I'm afraid but can commiserate. Like Howdy, many of the books I have read has not helped but I use a lot of the techniques she mentioned and they do help somewhat. The most effective for us is to try our absolute hardest not to react to nasty backtalk and get roped into a heated power struggle. Plus she can outwit me many times now. Also, praising directly and indirectly (mentioning in earshot to someone else) as loy58 mentioned works pretty well too.
I have noticed sleep/fatigue and hunger have huge effects (which is why I am worried about lack of sleep due to reading past bedtime - see my post).
Everyday is a struggle. It is so hard not take offense and stay calm! However, DD made major progress yesterday. In the midst of her intense attempt to make me change my mind, she abruptly stopped and counted to 5 seconds. Then told me that she used the technique we talked about to stop herself from calling me a "witch".
