You have it wrong. You are hearing yourself fluent when you are reading. If you can speak fluently while reading, you can speak fluently while speaking. The reason why you can't, it's in your mind. It takes mind training, learning techniques and etc. For example, pick a word that you have a hard time saying. Go to a mirror and practice saying it. Say it in a sentence. Speak into the mirror and the next time you speak to someone visualize yourself speaking into that mirror. It takes practice, it is not a magic pill, but it can be done. I became fluent after 50 years of stuttering and now I have helped many to become fluent. I cannot advertise it on Reddit because they call it self promoting. If anyone is interested, they can direct message me. It is not a gimmick.