Irishmaggie, if you can, I'd recommend pursuing an outside evaluation in parallel with the eval through the school. Some school psychologists are not well enough trained about autism to be able to recognize it in a gifted child, who may have very subtle language/communication impairments and present in unusual ways. A specialist is likely to give you much better information.
At the same time, you want the school to evaluate so that you can get the services.
It's a lot of work to do both, but worth gathering enough information that you have a really good picture of skills and challenges.
DeeDee