M8, I feel like the main reason why we stutter is not because of something physical or muscles being tense. It's because we are afraid of stuttering. Because i am 100% sure i am not alone on this. When i feel like im going to stutter or when i beg myself to not stutter that is when my stutter really happens. Idk just be confident and make the stutter your bitch. Try not to give a shit and project your voice, dont be afraid!.