The dynamic you are describing is about power. If you stutter less or not at all alone or with some people, then you have the ability to speak fluently. If you stutter in front of specific people (or types of people) you are giving them the power to make you stutter. Why should they have that power? What gives them the right? Do you have that power over them? Really think about the situations in which you find yourself stuttering a lot and analyze them. It’s often about power. Constantly remind yourself who has the power in your life and your speech. It’s you. It took me a long time to really understand this and I still have to remind myself of it sometimes.