Practice speaking in the morning. Pick a topic. Set a timer of 5 minutes, and talk about that topic, using slow speech. Do this throughout the day if you can. Set yourself challenges. "I'm going to go into this store, and ask for ____ using slow speech." Start with small things, build it up. Once you get used to using it when you're comfortable, start expanding into more challenging situations, using slower speech. Try develop a slower "inner talk" speed too. When you're reading, read slightly slower than you would now. When you're thinking, try to think slightly slower. This helps some people a lot. Practicing when you feel you don't need to is when you should practice this most. Make it become habitual and automatic. It will eventually work. Good luck! :)