Thats what it is. When you stutter or think about stuttering or try to resist stuttering you add "negative" emotions to your body. These negative emotions translate into tension when you are holding them. The more tension you have the harder it will be to speak. Overcoming this, is not about "stopping stuttering" but its about finding out why you are relating these emotions to your stutter and how to decrease them. Have you done any type of that work?