I've got the same thing going on! Usually if I've figured out something interesting I've gotta say it in the moment or else I'm never gonna be able to word it properly out loud. I'm great in writing, though. I think I just take some extra time to try to formulate my sentences- I can blank really easily and lose track of what I'm saying, which is fine enough on paper, but in real life I feel like I might come across as a bit of a clown.
For the people that really matter, I just ask for them to give me time to pause and think. Sometimes people can throw some really loaded statements at you really casually, and I need to ask them if I can think it through before we say anything else. If they're good for you, they'll take that time.