I talk fast too, especially when I get excited or nervous, and it always makes the stuttering worse. What has helped me more than anything is to force myself to slow down. A lot of times when I get stuck in a repetition of the same sound or a block, I'll make myself stop talking, take a deep breath, and begin talking at a much slower pace on the exhale. It can be forced. It can be awkward. A lot of times I even make weird gestures with my hands. Sure it may be weird for me to stop in mid-sentence, but it's a heck of a lot less weird than being stuck in one of those endless stuttering loops. And it almost always works for me. It takes a while to make yourself do it regularly though, especially when all you can think is "oh my gosh the person I'm talking to must think I'm crazy." But once I started I felt a lot better about my ability to talk to and in front of people.