... a mental brake that is. Here are some mind tricks when you speak too fast.
Imagine that your audience is comprised of 5 year olds and you have to explain some difficult concept to them. You must obviously go slowly so they can understand you. Force yourself to use difficult word combinations which will force you to slow down so that you don*t stutter over them. Do specific practice sessions concentrating on varying the speed of your delivery so that you get a better control over this aspect of your talks. Also, varying the speed makes you more interesting automatically. You must do these practice sessions out loud. To save time, they can be done in the car, or while doing your hair or jogging, etc. Cut out some of your material so that you do not feel rushed to get it all in. Going faster is usually futile because the retention level drops so low that you may as well have omitted the material in the first place.