Unlike some of these other comments, I think you need to bone up on your social skills. Exceling at work is about more than being good at your job. It's about fitting the culture, getting along with your coworkers, and being a good team member. If you isolate yourself, you're handicapping your career. You say you're kind of invisible for your managers. How often do you interact with them? How often do your other coworkers interact with them? I have a severe stutter and every day when I come in I say "Good morning" to my neighboring coworkers. I usually have trouble with it and don't particularly enjoy it, but I do it because it's polite, good social manners, and all that shows them I'm an amiable person, regardless of how easily I can communicate. In fact, I think the fact that they see me trying to be polite and social is more important than how it actually turns out. I would try to find situations that are easier, whether it's short one on one small talk or joining in on a group conversation and taking little steps to show them you're a good dude. Sometimes just showing up is enough, regardless if you talk a lot or barely at all. They do know you stutter, right?