Saw the head of Gastroenterology at the Hospital of the University of Pennsylvania for a second opinion on my tummy troubles. He doesn't think I have malabsorption. He will look into why my MCH and MCV values are slightly higher than normal. I don't drink much since my tummy won't tolerate it and these values have been elevated since childhood so it's not alcohol related.
As far as the B12, it's a bit indeterminate since I didn't get a blood test before I upped the supplements. He sees no harm in me continuing. For the D12 deficiency, he thinks it doesn't have anything to do with the GI tract. At our latitudes, it's more about getting adequate sunshine. He verifies that I have done all the standard tests: colonoscopy, endoscopy, capsule endoscopy. These all have shown nothing. Had a discussion about wheat/dairy intolerance that verified laying off the stuff is probably not a bad thing in terms of keeping tummy happy. No answer on fat malabsorption. So no more tests.
Digestive TractImage via Wikipedia
As far as a link between neurological problems and GI system, he feels that there is "fledgling science" to the notion that bacteria malfunctions in the digestive tract have some relationship to autism and neurological problems, but he won't take that notion into clinical practice, at this time.
In terms of managing my neurological problems, he thinks I am "doing all the right things". So, there. I have the good housekeeping seal of approval on my therapies.
Thus spake medical orthodoxy.