It will be imporatnt to continue with a systematic plan to manage the behavior, and the foundation of the plan should be time out. Don't expect that, after you discipline him, the problem behavior will immediately vanish. You've got to be consistent. Follow the guidelines in Lynn Clark's book SOS Help for Parents and you'll find success. As ana side, I'd stop any spamking. It will not be useful. Rely on the time out method in the book and you'll do just fine.
With the persistence of the problems, you might consider arranging an evaluation. The persistence itself does not necessarily indicate the presence of an emotional disorder, but you'll want to be sure.
I have had the same problems with my 4 year old son and have been following consistant guidelines for almost a year now. They do not seem to help him. Would you reccomend anything else for my son beyond discipline, and do you think he has a disorder of some kind? His behavior is similar, but more violent.