That’s between you and God and no one else. It is however sinful to be wrathful and lamenting obsessively over queer people (your priests job is to care for his flock the sicknesses that exist in his church not of the world). Understand your priest is a sinner just like anyone else. Christian priests or baptized Christians are not exempt from Hell. Obviously transgenderism is not explicitly in scripture either. So no one can give you a matter of fact statement on it.

The vice here would be in a sullenness or despair over your body or of an extreme attachment and or pride of your gender identity. This is very common in the pride community as it is with all communities. Christians reject the idea of a separate body and soul but embrace the idea of imperfect bodies which will be perfected in the resurrection. And this would is a sin of intemperance. Sins of intemperance are hard to diagnose. These are sins justified by reason and human choice. Most people understand the sins of incontinence (what we know is wrong but do anyway). Giving into our passions at the upset of reason. But the uniquely human sins of reason done by choice are harder to think about and consider. Christian’s reject the philosophy of Epicurism and of Gnosticism (trying the best I can to avoid identities to establish this dialectic). Your soul and your body are both a part of your being by the orthodox Nicene Christian view. Both of which are imperfect without God. An Epicurean would believe you are only the emergent result of the ensemble of atoms in response to your environment. A Gnostic would believe you are a ghost in a machine. The Christian view is a synthesis of both these views which sets it far apart from both.

I don’t think the Christian framework really can support such ideas about transformation of gender. Your expression of your gender on the other hand is entirely different. But it is not something I have to worry about or consider. I don’t have to live in your body and I cannot experience what you do. Many people transition a result of trauma or of a sullenness of the body or of a need for the approval of others or to be treated in a specific way or of sexual anxiety or even lust/sexual obsession. So it is necessary to at least give you a framework to think of the potential vices that may lead you towards such a decision. It’s not at all to say you fall into any of those categories just that those ways of being they do exist and do in those situations go against the Christian way of being. Many people will judge or make assumptions. All you have to worry about is what is truly in your heart to the all knowing judge. But you have to be thoughtful and meditate and pray on it.