I used to always speak too quickly...it's like my brain couldn't keep up with my mouth (or keyboard!)...I knew what I wanted to convey, but never chose the proper words, phrases or tones. Then I'd immediately say "Oh, I actually meant"...it bothered me so much because I know I was confusing people, and to some point angering them. It became a big problem at work back in the day.
I had to train myself to stop speaking so fast and to stop for a moment before saying something. I developed that filter, but it took a lot of practice. I'm lucky in a way because I speak both English and French, so my method was to try and translate into French what I was thinking in English. It forced me to choose the right words for the situation.
I still say things I shouldn't...I was reminded of that yesterday and to be honest, it didn't even dawn on me...like, I always say "I'm sorry" for nearly everything where I have no need for apology.
The old no-filter speak sneaks out too sometimes, under high stress and anxiety. I've said many things I don't mean when I'm feeling panic. Now that, I'm not sure how to fix.