I find it really hard to shut up as well. My massive ego always tries to convince me that my opinion is invaluable - even when others really don't need to hear it, and really it's just a way of airing my own resentments; fears; or anxieties.
Anyway - recently I heard someone else say he'd been told by his sponsor to do something to get past just that problem, so I've been trying it, and it's been quite helpful to me (not 100% success rate - but I'm getting there).
He said "I was told, before you open that big mouth of yours to give an opinion or repeat what you've been told, just ask yourself three questions. One. Does this need to be said? Two. Does it need to be said by me? Three. Does it need to be said by me, right now? If the answer to any of these questions is 'No', then keep quiet."
It's really tough, but I never seem to regret not saying things in the same way I do if I let my wobbly-gob run away with me.