Thats the great irony of it, not you, but your very body has to not care, a word has to become any other word but that may take some serious attitude change or a lot of experience of not caring, feeling the fear, the stutter, doing it anyway.  Until the body truly doesn't care what happens and all of a sudden that word or sound becomes like any other.  The problem, the great irony is you do care, its bothering you so much, you refuse to accept it.  So how do you start?  You said it yourself, its anxiety based down to its very core sometimes, the moment someone asks you to repeat something you may have said just fine, etc....so how do you care so much and want to stop that anxiety at the same time?   You set the rules so you tell us, what will you do?