Actually the opposite. It’s been my experience that people who stutter have above average intelligence. I always thought, it was because our brains are constantly at work monitoring our speech and constantly adjusting to try and avoid blocks. And the brain is like a muscle, you exercise it and it will get stronger. The trouble is that it’s a lot of wasted CPU cycles to constantly monitor our speech. This lack of focus might simply just be ADHD or something similar. You should speak to a psychiatrist and get tested.