John, you are doing the right things!

Your B12 level of 350 before supplementing is certainly in the suspicious range, so keep on taking the B12 (preferably 1000-2000mcg daily of methylcobalamin) daily... forever. Be sure you are taking extra B-complex, too. Omega 3's can be helpful. Also, you might want to check on your zinc/copper levels. "no zinc - no think" You can overdo on zinc, so check with your doctor, or keep it to 25mg daily.

It can take a long time to recover from some of the cognitive effects of a B12 deficiency. My memory was very very bad at my worst, which came three years after the onset of my early symptoms... with a B12 level of "low normal" 294. I couldn't think, period. I had trouble with following and participating in conversations, etc. I did all sorts of brainless things. Even though they say most improvement comes within 6-12 months, I know I continued to improve for years.... especially with the cognitive issues. I had brain fog, memory problems, word finding problems, concentration problems, etc., and all are much, much better. Now, I can probably blame it on normal aging.

Also, try to force yourself to USE your brain... actively work on memory tasks. I know it is hard work, but it helps. Unfortunately, I didn't think to do that until several years after the fact. Now I play games on a Nintendo DS, like BrainAge, and Word games. Math problems, crossword puzzles, "concentration" type card games to remember matches... anything that forces you to use it... so you don't lose it. I've been amazed by how much quicker and better I can think when I'm playing those BrainAge games.

Gluten free needs to be 100% strict to be effective. A little bit does hurt, and may prevent you from seeing any improvement. So, hopefully getting more stingent about that will pay off. Healing nerves and the brain is slow business; brain fog symptoms may clear a little sooner.... but still, it could take 6-12 months to see improvement. It may come sooner.

Many people have the same problems with casein... or other foods. There may be others you need to remove.

Not a bad idea to get checked out for candida. It often goes hand in hand. A gluten free, casein free, sugar free diet goes a long way to snuff it out, but you may need an anti-fungal if it is a problem.

Good luck. Stick with it!