It has been reported in the stuttering research for about 80 years that people who stutter are remarkably more fluent when they are alone. So you are not alone, in fact you are perfectly typical. Most recently, Prof. Eric Jackson et al. showed that people who stutter are, in fact, almost PERFECTLY fluent if they truly believed that no one could hear, or record, their speech, that is, they were in a "private speech" conversational environment. See Jackson et al, "Adults who stutter do not stutter during private speech", Journal of Fluency Disorders (2021) 105878.