I believe it is about quality vs. quantity.

I have similar traits. People often tell me that I do not speak enough. However, whenever I do say something, people find it novel, valuable, insightful, and nearly always correct.

Once people get to know me well, they start working around this to hear my points of view, and that they keep coming back indicates that I am truly adding good value to them.

I am both a good listener and a reader, and in fact a good speaker and writer too.

However, the quality I produce comes at a time cost as a result of which I am not real-time and nor perceived as speaking 'enough'.

-- The following are things that have generally helped:--

* Do pre-work whenever feasible. This reduces the mental processing power needed in real-time.

{Now once the meeting begins and I am not the initiator, I may only be listening and observing what all things are being missed in the discussions, what common confusions or the hidden assumptions are.}

* Even if not, consider yourself as the owner of the meeting discussion. Assume that if good conclusions or decisions are not coming, it would be your own fault. This helps to participate in a meeting more effectively, even making a callout to slow down the discussion if needed. At times, you may direct the current meeting at understanding the problem better, and invite a follow up meeting for the actual resolution.

* Fine-tune yourself between answering and asking questions. If I already have good thoughts, I may be illuminating others, clarifying, answering, and moderating the discussion. If not, I may be asking the questions on my mind, say to probe assumptions or just to fill my knowledge gaps.

* Making keyword-level notes during the meeting helps. You cannot spend the time writing details as then the needed meeting participation time and attention are lost. Having short notes however helps to bring needed things back into mind quickly. Some people naturally do better at this, having good short-term and long-term memory.

* Use body language to indicate space needed to speak up. During the meeting, I may slowly stand up in a corner or walk up to a whiteboard, aiming to grab speaking time. Being in a standing position helps (it's a body language thing).

* Another important but tricky piece is the time gap between people taking turns to speak. Wait too long, and someone else may start speaking. Wait too short, you may be cutting the cirrent speaker short. Raising hand here helps if nothing else. If I find someone else starts speaking but that is only taking a wrong turn (e.g., incorrect hidden assumption, or going off-topic), I may grab the speaker position by clarifying exactly that (E.g., "we just spoke about this but I think there is a more fundamental thing we need to consider. {It goes here.}")

* Needless to say practice and experience helps.

* If there are no clear goals for a meeting, just general chit chat between a large group of people, it gets harder, however the similar techniques as the above help.

Overall, as far as you are maintaining good quality in what you say, don't consider being slow as a loss. It hurts the most only for the first few months on a new team or group as people are getting to know you better.