It took care of itself. My DS spoke non-stop as a toddler/pre-schooler. His lovely preschool was good about it, but he was a serious chatterbox. He had a few issues in Kindergarten, but not many, and quite honestly, the minute he started to read, things got really quiet around here.
It will take care of itself, I think. I suggest you start a conversation with him about the social issues around constant talking,etc. and just start to make him aware of what is going on. I wouldn't place any judgments on the talking at this stage, just encourage him to observe what he is doing. I bet it won't be an issue by 5.5, but if in a year things haven't settled down, you will still have time to think about how to address it.
Cat