As I understand it, there is a phenomenon among transgender people where no matter what they do they can't help but ask themselves the question, "Am I really an [insert self-reported gender category here]?"

The obvious answer is "No". In fact this experience seems suspiciously like trying to make oneself belief that one believes one's gender to be X.

Humans universally make inferences about their typicality with respect to their self-reported gender. Check Google Scholar for 'self-perceived gender typicality' for further reading. So when I refer to a transman, by my model, I mean, "A human whose self-reporting algorithm returns the gender category 'male', but whose self-perceived gender typicality checker returns 'Highly atypical!'"

And the word 'human' at the beginning of that sentence is important. I do not mean "A human that is secretly, essentially a girl," or "A human that is secretly, essentially a boy,"; I just mean a human. I postulate that there are not boy typicality checkers and girl typicality checkers; there are typicality checkers that take an arbitrary gender category as input and return a measure of that human's self-perceived typicality with regard to the category.

While we're assigning categories in complete defiance to common sense and evidence, why are we so sure that the category "human" is applicable?