The consciously slowing down is the cause. The more you make yourself hyper aware that you will stutter the more you'll stutter. Its really hard to do and you need to just pretend at first but just give it a go for a week or so and we if it works. Try to focus on reducing your anxiety about your stutter. Just try to act nonchalant about your stutter and don't give it the psychological power over you. The more you can reduce your anxiety around it the better off you'll be. It won't go away but it'll probably decrease and definitely improve your quality of life. Whenever my stutter is a bit worse then usual. I just do some breathing exercises for relaxation(not for speech) every day for a few days and it always improves.