My brain works the exact same way. Your stutter might by psychophysiological like mine. We place subconscious value on certain words which causes the stutter a lot of times. That's why names, numbers, titles, etc, are so hard to say - you can't change them. That subtle pressure to get the word right makes us overthink and we make the word too important. So when we practice presentations, etc, it's like suicide for our speech. We're giving EVERY word value, EVERY word is irreplaceable. To overcome this I would give myself notes, and just speak from memory based off of the notes. No way I'm writing a script for myself and then reading it, haha, no way. The less I think about what I'm saying the more fluent I'll be. That's why when I speak or read, something that helps is always focusing on the NEXT word you're going to say. Keeps your attention away from the words on your lips and it eliminates the otherthinking. Hard to do but it does help quite a lot!