Have you tried speech therapy? Don't just go to one and write it off, there's good speech therapists and bad ones. I've had the whole "Taaaaalllllk llliiiiike thiiiiiiis sooo yooouuuu dooonnn't stuuuuteeeerr." crap before, but the speech therapist I'm seeing right now has taught me techniques others have not, and encourages me to speak as quickly as is comfortable for me so the technique usage is not obvious. Try a few different ones.