I would try straight up probiotics, with a variety of bacterial strains. I heard the kinds in the dark, glass jars is best. Also a B-vitamin supplement, and maybe bitters (genitan) to stimulate digestion. I love ginger for digestion, but it didn't seem to help as much for me during my latest stomach attack issues (it has worked well before...I usually just eat fresh, raw ginger or else the picked ginger that is eaten with sushi). These measures have often helped with my digestive issues in the past (thought I may have gastroparesis, too, but am going to go to the doctor for a workup).
Custom blended powdered herbs have also worked well for me. I get them at during acupuncture appointments, but last time I only went in for a herbal consult. You may want to consider that route.