Comment by tombert

I'm the same way, I speak super fast pretty much all the time, and it can be hard for people to understand me if they're not used to it (and I don't blame them).

What really helped for me (and I realize that this doesn't scale to everyone) was lecturing for two semesters. I had pretty good motivation to slow down when students' grades and futures depended on understanding what I'm saying.

I didn't realize how much this helped until I presented at a conference after I was finished teaching, and I realized about midway through my talk that I was speaking considerably slower than I usually did at these things, because it turns out that public speaking and lecturing aren't actually that different.