Craig: Not to scare you, but have you explored the possibility that your child has mild to moderate autism? The behavior, especially at his current age, doesn't sound particularly normal, and your son reminds me of students that I have encountered with autism and a good friend's daughter who is autistic.
http://www.childbrain.com/pddq5.shtml
http://www.childbrain.com/pddq3.shtml