My experience, based on a rather small sample, is that there is a strong overlap between being on the Spectrum and having at least some doubts about ones gender identity. Possibly our lack of social awareness (= tact) means we are more ready to admit to something that most people would keep well hidden. Possibly there is a real correlation.
At one point I found that of the four male Aspies regularly posting to a small forum, three had well developed female personas. Too small a sample, but interesting. Another forum member was a paintball ref and really one of the lads (and female).
Anyone else willing to speak for themselves? Any parents noticed boyish girls or girlish boys?
"concern about their self-identity in general" - which could include gender identity. Plus my point that we are likely to talk about something that it is "not done" to talk about. That might mean there is not so large an overlap as I thought, but might not.
I was a volunteer for a research project recently that specifically wanted people on the Autistic Spectrum with Gender Identity issues. A small population, but they got their volunteers.