If you don't mind me asking, what were the observations that lead you to locate and consider that hypothesis in the first place, and how did you come to reject it?

For my part, I've been trying always to hug the query as tightly as possible; when I can get myself to stop thinking abstractly and verbally about whether or not I'm "transgender" and instead wonder perceptually and at the object level about individual, separable questions such as "Have I ever been happy about becoming more masculine?" (if not, I don't have to, whether or not I am "transgender"), "Do I feel more comfortable being referred to and addressed as male or female?" (if the latter, I can continue going by my new name and pronouns, whether or not I am "transgender"), "Am I happy about the changes I'm undergoing/anticipating; do I feel better overall?" (~7 weeks HRT so far; if so, I can continue as long as it continues to enhappy me, whether or not blahblahblah), "Do I prefer speaking in a female voice?" (since voice feminization is just a matter of training anyway and doesn't remove manvoice, I am free to develop a female speaking (and preferably singing) voice and use it as much or as little as I find I want to), etc., the answers are always pretty unambiguous, particularly since I would have no problem with myself turning out to be genderfluid (which I had assumed I'd be for a long while, though I didn't learn the word until this year) or bigender or otherwise nonbinary. But apparently I'm not, at least given what I know so far; not since I started letting myself think about such things have I woken up feeling any desire to be or present as more male that day than I have to, never have I felt like tying back (let alone cutting off) my long beautiful hair since I got it permanently straightened (it has more of a scruffy-male-hobo look when it's not straightened), ne'er since I got my current one pair of girl jeans have I felt like wearing guy clothes, except when going out (I'm not able to pass yet), and I always change back as soon as I get back home, and the feeling is just kind of like "Well, why the hell wouldn't I?". Same with things like body hair, once I got rid of it for the first time, I've never felt the need to consider whether I want to let it grow back, it doesn't even feel like a question. And as for HRT itself, at this point I don't think I could stop if I tried, I don't think I could even try to stop if I tried, because I just don't have any desire to at any level. My understanding is that cis males generally would not appreciate the breast growth and diminished sex drive.

How far would you have gotten using a process like that?

Huh, I wonder how I missed this post the first time around; I was already questioning my gender when it was posted. (It sounds like I'm in the same boat you were in two years ago; 21, biologically male, feel like I'm almost definitely trans (several other similar details too), but still have a lot of "And yet..."s.)

The way it stands now, the so-called gender identity disorder isn't really something that is truly diagnosed, because it's based on self-reporting; you cannot look into someone's head and say "you're definitely transsexual" without their conscious understanding of themselves and their consent. So it seems to me outside the domain of psychiatry in the first place. I've heard some transpeople voice hope that there could be a device that could scan the part of the brain responsible for gender identity and say "yes, this one is definitely trans" and "no, this one definitely isn't". But to me, the prospect of such a device horrifies me even in principle. What if the device conflicts their self-reporting? (I suspect I'm anxious about the possibility of it filtering me, specifically.) What should we consider more reliable -- the machine or self-reporting?

This prospect actually isn't only hypothetical; there's been some research showing measurable differences in pre-transition trans people's biology, including brain structures that actually appear to resemble those of the sex associated with their self-identified gender. This is quite interesting, and if true, suggests that genders (not just sexes) are more like natural categories than I previously thought. I'm looking forward to seeing more research done on this. And although I definitely wouldn't advocate replacing self-reporting with brain scanning unless we had a comprehensively worked-out theory of how gender identity actually worked and we could actually predict people's eventual gender identities and outcomes better than they subjectively could, it would at least be good in the meantime if it became possible to probabilistically screen children for likely transsexuality so that puberty could be delayed if necessary.

Anyway, I considered such a device as a thought experiment during my own questioning, and I noticed that I too would be hoping that it would say "Yeah, you're definitely trans" and would feel despondent if it said I had to remain male. But that kind of gives the game away, doesn't it? I can't think of any instance where a non-trans person would be wishing or hoping they were trans (at least after reading as much about it as I have now); it's not a life that anyone would wish upon themselves. I intercepted some other motivated reasoning during my questioning, but all of it was along similar lines — "I hope I don't conclude I'm not trans, because then I won't get to be a girl, and I really want to be a girl." I'm not saying I'd embrace motivated reasoning in this case, but this case is unusual in that observing that you're engaging in motivated reasoning toward a particular conclusion is actually at least some evidence for that conclusion. (Makes it hard to know how much to update by, though.)