KatieM, we actually had a child behavioural specialist come to the house to help us deal with DS6's behaviour when he was three and a half years old, and it was pretty much exactly for all the issues you describe. I think his behaviour was/is probably attributable to a number of factors: his intensity, his strong desire for everything to be "accurate" (because of his perfectionism, I guess), and the fact that he truly needed to understand "why" we were supposed to be the ones in control (the explanation that satisfied him was that as his parents, we would go to jail if we didn't do a proper job of keeping him safe and healthy). Also, apparently GC often experience a great deal of frustration because they have a deeper understanding of the world around them without necessarily having the emotional maturity to deal with it.
Of course, just because you understand where it's coming from doesn't mean that it's any easier! Anyway, she was basically a parenting coach and provided us really invaluable help. He's doing much better now, though we definitely still experience some tough periods...
