My 2 cents. Ive tried techniques and I experience the "downward spiral". Where I hit that first significant block and all of my thoughts are muddled and I turn on survival mode and try to brute force it. After a lot of self help and support groups, I realized for me the techniques are rendered worthless if I am not accepting of my stutter, and more importantly, recognizing the fear. Facing fear was the missing piece for me. I would suggest trying psychotherapy to work on the anxiety and do something like CBT. The mindset needs to be changed from the stuttering mindset. An SLP can help to an extent as well, with voluntary stuttering and avoidance reduction