I'm willing to bet that lots of socially anxious folks -- even those with large vocabularies -- mispronounce lots of words. And that's largely because we seldom interact with anyone in person.
I'm like this and I had an extremely intelligent girlfriend some years ago who was like this. I've a larger-than-average vocabulary, yet every once in a while I'll embarrass myself by mispronouncing quite common words.
Edit: damn, I meant to add a poll to this. Looks like now I can't add one . . .