Something worth trying: get a friend to read aloud at the same time as you. It sounds stupid, but when I do this I don't stammer at all. It has something about imitating the other person's breathing pattern; if I read the same passage out by myself, the stammering returns. For me, this helped realize that I stammer mainly because I don't exhale in even flow when I talk. The stammering comes because I keep holding my breath (my stammer is mostly block, not repetition). Now I work on exhaling fluidly and breathing from the stomach.