Gender Identity. One is a woman/man trapped in the wrong body and attempting to live full-time in their new role. The goal is to transition into a new life.
Drag queens typically have no interest in transitioning. They're men and relatively happy about it, they just crossdress for...oh, any number of reasons, it doesn't really matter. They're men, identify as men, and have no particular interest in living as a woman.
Though I've heard of some transsexuals attempting to earn money by acting as a Drag Queen, those scenarios are rare enough to not be particularly relevant.
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"We like to think the past doesn't have any effect on us, but ignorance of the past can be as dangerous as a ticking bomb."