Stutter when i think rapidly

Stutter when i think rapidly Bare with me as I describe my problem. I'm 6'3" and weigh about 150 kg age 28. When I was a teen I loved to chatter about anything I could think of, and because of this my teachers in school used to say that I should talk "quietly" this had made me self conscious about my voice has led to MUMBLING STUTTERING and a higher rate of speech with little coherence. Now I have researched a lot and to a few exercises but still can't fully understand them If you guys could either provide links to better breathing exercises or any regime you guys go through everyday, it would be really appreciated for stuttering and mumbling with higher rate of speech