He definitely has a stutter, he's spoken about it over his career many times. A quick Google search can reveal this. Also stutterers are pretty quick to recognize when someone else has a stutter. He has one. Do you stutter yourself? If so, you'd know that swapping words, by accident, is pretty common. That being said, I do think most of his gaffes these days from him are due to his diminished mental capacity, not his stutter.