Leviticus 20:13 (KJV)
13 If a man also lie with mankind, as he lieth with a woman, both of them have committed an abomination: they shall surely be put to death; their blood shall be upon them.
The above verse is the one you're referring to, right? In that case, my opinions on this are, more or less complicated. I do believe that sex was originally intended for a man and a woman to begin with before the Fall, and I do still believe that is God's ideal. However, I'm not sure if I'd call it sinful. As of right now, I believe that two men, or even two women can be under a covenant, and God would allow for that. I'm just referring to those who identify as a same-gender couple. When you add being transgender, and even biological sexes in the mix, the theological implications can get a bit trickier.
I do not believe being transgender is a sin. As it stands (for me), I personally believe it is a product of the Fall, much like I believe that me having to wear glasses is a product of the Fall as well. There is a specific passage in Exodus that has me considering otherwise, but I need to look into that more before coming to a more concrete conclusion. As a transgender Christian, I personally believe that I must try to live my life out as a godly man. It doesn't always work out like that, but I'm trying. I'm non-transitioning right now, so that makes it harder for me to actually put that out in practice, but spiritually, I at least try. I know that if/when I ever find a wife, I will jump start my transition so I can better live out God's will and reach His ideal for a union as much as I can.