Thank you very much for your response, Chris.
We seem to see a decrease in his tic when dairy and gluten are strictly avoided after a little more than a week. However, I am still not sure.
The allergist we saw last week was of no help, simply prescribed nasal spray (he preferred the steroid kind). Needless to say, we did not go that route. It seems quite the journey, but we are determined to find out what will be best for our son. Again, thank you so much for your reply!