Our son did the same thing at around 3. His brain was moving faster than his mouth. But then it stopped, without a lot of fanfare.
When he entered kindergarten, they had all kids tested for all sorts of things so they could start with a good baseline of info. He went in the room the same time as a bunch of kids but didn't come out and didn't come out. I began to get a little concerned. When he finally came out, the speech pathologist looked at me deadpan, with a little twinkle in her eyes, and said, "He won't be needing my services." She said she kept giving him more words but she couldn't stump him--his vocabulary was too big. : )
The strange thing is that when he started middle school, he started stuttering again. Two years later, he still does it when he gets excited. Truth be told, I think he's been going through a huge growth spurt again and his brain is on information overload.
I went to a workshop recently that said pre-teens and teens revert back to some of the phenomena that 2-3 year olds have. Huge bursts of growth, hormonal bursts, and emotions galore. It certainly fits our son right now, so I'm hoping this will pass as well. But I'm keeping an eye on it.
Maybe it's time to try the turtle talk thing. I liked that and I think he would, too. In fact, he just got home a bit ago, and when I went down to say hi, he was doing an exaggerated slow-motion walk across the kitchen floor. This might be right up his alley!
Hail to the turtle talkers!