taking gluten out of my son's diet made him "calmer"...or rather when he gets gluten within an hour he becomes MUCH more quicker to anger and more intense.
You of course do not need an expensive test to try the diet. With my son I just made a list of all the foods he eats that are gluten free and just gave him those foods. We are low dairy but he does get cheese occasionally and on pizza, but no other dairy. Dairy didn't seem to make a difference, but if he gets a lot of icecream or a couple days in a row I see a change in is irritability.
Have you done a food allergy test? Finding out my son's food allergies made a big difference in his healthy (of course) and his behavior.

My little one has non-celiac gluten intolerance. She was off-the-charts small until we switched her to GFCF, and then she had a dramatic "catch-up" weight and height gain (went from wearing a size 18 mos. to a 4T in 5 months). This despite testing negative twice for celiac (2nd time extended panel) and wheat allergies (again 2nd time extended panel). The couple of weeks on GFCF were rough but then it became easier. She also went from being a super-picky eater to eating a wide variety of foods. We actually didn't see an improvement in her ASD symptoms, but the physical response was so dramatic that we have kept her on GFCF.

sorry took me so long to answer. yes, he is on a probiotic, but I'm not sure it's enough. I'm putting Culturelle for kids in his juice every morning. I've been consulting the nutritional therapist, Judy Converse, and in her book she said kids like Chase need at least 8 billion CFU (not sure what that means), and the Culturelle only provides 1.5 billion.
There is a testing kit you can buy for stool samples - Judy says that traditional doctors do not test with the kind of detail that this one does. I can give out the link if anyone wants it. Might be worth it to read her book "Special Needs Kids Eat Right." She explains all this in great detail.

i'm confused what counts as constipation. my son only goes once every two or three days, but when he finally does, it's normal looking and is no struggle to release.

What is a GAPS diet?