As someone mentioned, correlation doesn’t equal causation. It could be any number of life or neurological changes other than testosterone. It can be completely random. You’re likely biased because you want to believe your stutter is based on a masculine characteristic. It doesn’t make you more masculine or less masculine. The sooner you accept it’s merely a random quirk, the sooner you’ll be more comfortable with it, and the less prominent it will become. If it’s any reassurance, people are noticing your gains more than they’re noticing your stutter.