We had a good experience working with Dr Mitchell in DC (from the DAN! website), as he and his partner took a holistic look at my childs environmental allergies, food sensitives, as well as oddly enough the influx of yeast in her gut... all to help out with her ASD traits and low speach. Things are getting better slowly, but improving - she is a "slow responder"
Also, you should do some research on this prior to cutting anything out of your child's diet. Kids need calcium and vit D from milk - we use darifree which I order from online, expensive but good. In order for the diet to work as well you need to eliminate all casein, even mixed into things (which is tricky).
I recommend the book; Special Needs Kids Eat Right, by Judy Converse Rd/LD/MPH