Understanding the language of your mind, the images we present to ourselves, the meaning we place on these images and certain events etc are all important aspects of understanding the problem. Just trust me with this and answer me honestly now. When you envisioned yourself speaking fluently (it could be past or present or in the future) was the qualities of the image not better? If you honestly compare the two images the one of you blocking and the one of you stuttering you'll notice the differences in the two different images, how they present themselves physically etc. Your mind has created this stuttering matrix if you will and this "matrix" has a life of its own. It may seem meaningless to ask you these things but it really isn't. The image you had of you blocking already tells me you have a horrible relationship with blocking. That's okay though I'm the same but there is hope.