I think you should be more open about your stutter. I recognize a lot in your post. I was also covert and very afraid of certain letters witch I know I block on. Since I be more open about my stutter and don't substitute letters anymore the difficult letters a not so scary anymore. I know I'm gonna stutter and most of the time it's okay for me. Most of the time the listener know I stutter so when I block it's not a big deal. I know it's a difficult road, but at the end it is all worth it.