Acting is by definition not being yourself. I'm not sure which purpose it would serve to train in acting, since you're going to have to be yourself outside of it. Unless you intend to not be yourself, which I don't think is anything that should be recommended. Stutter variance is hard to get used to, but it's an important feature to keep in mind, when having a stutter. Training for improvement, without doing it in the manner of speech therapy, is not going to be a reliable route. Or in other words - we don't _pretend_ to be confident. If you feel less confident than you'd like, this is something you should address specifically and directly. Don't try to hide or lie about it.