I have the same problem. Especially if I get over-excited or angry or stressed. Some times the words come out jumbled because my focus will change mid-word. More often my mouth just won’t form the words and I have to calm myself before I can speak. I also have a problem with stuttering. The funny thing is that I really enjoy and am good at public speaking! Go figure! Even so, speech can be a real source of frustration for me.