You already know it can be strenuous work, but the few women do great jobs. You'll loose muscle mass and strength if you start HRT in the future, although everyone seems to adjust in time.
I know 3 mechanics who worked for Toyota, Chrysler, and Jeep. They said dealer shops want good motivated and ON TIME people. Good mechanics are always in demand, while the ones who take too much time on a job or always need help don't have the same kind of job opportunities. I don't think gender is an issue in dealer shops, but in private ones a woman in coveralls might have a hard time if customers don't like her.
No idea what it's like in the South. But here in a far north conservative Christian area almost all transgender individuals have moved to friendlier places like SF, LA, NY, Seattle, and Portland.
But if a trans mechanic worked around here I'd send work her way.