I’ve stammered (as we call it in the UK) all my life but it was only about ten years ago that I saw a therapist who really turned things around for me. The big revelation was that the things I had always thought were the stammer - the facial tics, eye closing, scrunched up face etc - were actually secondary behaviours that I’d adopted from an early age to try to tackle it whilst talking. If you can train yourself out of doing that, it’s much less stressful to talk.