I'm amazed - nobody yet has suggested you read "The Explosive Child" by Ross Greene!
I'm not being sarcastic - it's just that so often when someone new comes along, especially with what you describe, this is one of the first suggestions...
OK, get the book. Borrow it from a library if you don't want to fork out for a copy just yet. Also, check "Early Childhood to see if there is still some discussion on the book there.
It's a darn good book, it shows how you often need to change how you handle a kid, to avoid the oppositional-type behaviours. It's not for everybody, just a lot of people here. For us, it helped a lot.
What you need to do, apart from getting that "Asperger's traits" given a more formal label, is get into his head and find out where he is coming from. If he has Asperger's in any way, he is far less capable than the people around him, to think from their point of view. These kids often seem to be very oppositional, when they simply need to understand. You can't just dictate to them, they will dish out the behaviour dished up to them. And if you think about it, a lot of standard discipline involves, "Because I said so, that's why."
For a kid like this, it's a disaster. An Aspie kid given the "I'm the parent, do it my way" will dish it back without thinking about it. After all, you are the person who is teaching him how to behave, surely you just set an example? But then he comes out with, "Well, you sure took your time! I've been waiting here for half an hour for that glass of milk I asked for, what have you been doing with your time?" and then wonders why we get angry.
Next time you hear your child being "oppositional", listen to what he says and how he says it. Can you identify where he heard that?
With these kids you need a different tack. Ross Greene explains some really good options that are NOT hard work (although you need to keep your mind on the task and not slip back into old habits). We found our life was much easier, although sometimes people look askance at us when they hear difficult child 3 apparently get away with stuff they wouldn't countenance. To an Aspie, there is no such thing as authority. Everyone is equal. The fact that some people insist on being listened to and having priority (such as teachers, bosses, parents) is a mystery, they can't understand why. To them it seems to be injustice and especially bright kids will really resent what they perceive to be injustice.
To get a feel for Asperger's and related conditions, have a look at
http://www.childbrain.com and do their online Pervasive Developmental Disorder (PDD) questionnaire. It's not diagnostic, it's just a guideline, something for you to think about. You can print the results and show the doctor, to give the doctor something to think about as well.
Welcome to the gang!
Marg