so glad you are here, bsmom! Sounds like you are living with a child much like my son, who is now 13.
It sounds like you will need the advice of a good professional. Many of his behaviors do seem 'typical' for a gifted child, but having tantrums when told what to do or to not do is a problem. I do think that it is important to find how 'if and how much' he is gifted in the course of solving the tantrum thing.
Question: Do these tantrums happen only at school or also at home and when he is with older children?
Question: how many hours does he spend in Pre-K?
Question: Does the family need him to be there, or are you sending him simply so that he will be 'ready' for Kindy? There is a funny idea circulating that children 'must' do preschool so that they won't be at a disadvantage later in K. If this your main reason for having him in school, you might need to 'check your premises.' Can you get the school to allow him to spend all or part of his day with the older kids?
Question: Which books have you read? I would especially reccomend -
http://www.energyparenting.com/products/item15.cfm which is one approach to parenting that has worked for me with my gifted/ intense and possible ADHD kid
and
-http://www.giftedbooks.com/productdetails.asp?id=48
which will help you know how important it is to have your son's testing done by a recognized expert in the field of unusually gifted kids.
I 'go ni-ni now' and look forward to more reading and typing tomorrow.
Best Wishes,
Grinity