"Mayo diagnosed me with SIBO twice. Two unsuccessful 2 week rounds of xifaxan. After extensive testing with no definitive answers for multiple gastro/neurological problems, I continue to have symptoms of IBS and SIBO."

That is because you did not find and get rid of the food source of your SIBO. In my case it what whey protein I take for lifting weights. Switched to beef protein shakes and problem solved.