My answer remains the same as in the above post with the following addition:
If your son's GI is dismissing the firmly positive DGP IgA without a complete celiac blood panel, refusing the need for a biopsy and providing no alternate reason for the positive DGP - it is time to look for another doctor. I'd highly suggest you look for a Gastroenterologist that has both training and experience in Celiac Disease.
If I am reading your posts correctly - your son still has not had the following celiac testing:
...it wouldn't hurt to get the entire panel drawn again along with nutrient testing (to uncover possible malabsorption issues) if it has not done to compare with his previous numbers.
your list would then be:
Total Serum IgA
I would add AGA - both IgA and IgG
B12, D, K, Iron, Ferritin, Copper and Zinc
If you are not wanting an endoscopy - have the blood drawn one more time (his primary can order these tests) and then remove ALL gluten from his diet and watch for symptom resolution.