It sounds to me like you’ve benefited from speech therapy a number of times in the past. Have you practiced the techniques you’ve learnt in the past whilst alone, reading aloud at slower rates, in unison with a metronome or other external timing source? Gradually pick up the rate whilst consciously utilising on the techniques. You could even try tapping the side of your leg whilst talking as it gives your brain an external timing source to sync with as you speak. The internal motor timing mechanism in our speech motor networks is dysfunctional, so sometimes using an external timing source helps a lot! That’s why we do not stutter when singing… we’re using the timing of the song to sync and link our words. It’ll then become second nature to you and you’ll block less. Ok so it won’t cure you completely but it’ll improve your fluency to the point where a random block here and there won’t bother you, or your audience.