Have you ever tried speech therapy? I naturally grew out of mine but it was pretty severe when I was young and still pops out every now and then. Usually when I’m anxious. Anything you can do to relax is helpful before a situation that you are anticipating having trouble. In any case, just wanted you to know you’re not alone and I understand exactly how you feel. You are not stupid. People are awful about it, I agree. It’s 100% a speech fluency inside and not and intellectual disability.