J.C.
My son used to be the same way. We found that teaching him how to verbalize emotions some has helped. If we see him act out, we stop and ask him what he was feeling and give him some possibilities. To help him understand, we explain them a little. For example, we'll ask "Were you sad like..." and then whimper and pretend to cry. For excited we'll cheer like we're at a sports game, or like we've just opened a present. As he learns the emotions, we don't need to keep acting them out. Also, talking to the preschool can help. Sometimes they can help more because he will constantly be in situations where he needs to be easy with others, and they can help show his how, and can maybe give you some more ideas, too.