Thats interesting. But it makes sense. This could be due to you not attaching your self worth what you read outloud. But when you are talking, these are your words, so automatically gives the ability to be judged on what you say. Causing more tension and ultimately stuttering more. Take for example people who stutter on purpose in order to desensitize themselves to stuttering.. They often feel amazing after they stuttered on purpose because they just faced their fears and heightens their emotion state. But often times this "good feeling" does not translate over to real stuttering, not on purpose. Often times, the "real" stutter attacks their self worth, self esteem and makes them feel inferior. But in both instances, stuttered on purpose or not, they still stuttered. The only difference is the attachment of ones self with the outcome or judgements of others. I believe its the same with your situation. There's a lot less pressure be perfect, because even if you say some crazy stuff, that was on the writing, that wasn't you. So your ego or self image does not get attacked like it would if someone where to judge you for what you actually said. And as a defense mechanism you tighten up, try to be cool, try to say the right things etc. All in which puts you in your head and makes you stutter more. Fin.