i feel im the same way, i dont stutter while i read and usually i read aloud, if not under my breath. i think its easier to speak in the absence of others because we arent feeling the subconscious social forces when talking to a page i had to write a short paper on speech disfluency and social inhibition for a class and this was one of my favorite journals i used while writing, a lot of social psych terminology but i felt shed some light https://www.sciencedirect.com/science/article/pii/S0094730X21000577