The variable is knowing people are listening... Could you try this experiment and tell us the results? Pick a subject that requires you to speak about a topic you are knowledgeable about or just your feelings; it does not matter as long as you can talk for a while. Close your eyes and start speaking... Keep your eyes closed... Have someone you live with come in the room at a random given time, but have them be quiet. Open your eyes after a few minutes, and the person there must have heard you speaking fluently. So, if you are physically able to speak fluently, continue talking in front of someone to see if you can remain fluent. My theory is that you can speak without stuttering, but you have severe social anxiety that disrupts your speech and thought process. Maybe practicing the closed-eye technique can build confidence and allow you to speak fluently once you eliminate social anxiety.