I was the same didn’t display any hyperactivity when I was younger! But my stuttering was personally for me due to racing thoughts and not slowing down enough. I take Vyvanse 40mg at the moment and find that I’m able to focus on what the person is saying and in turn when they ask me questions I don’t stutter as I’m focused on the now rather than anything else. It’s helped me become more confident in speaking also. For me I think stuttering was due to anxiety from ADHD not being treated.