Ok this is a little weird but I thought I'd throw it out there. I'd been having numb hands and none of the normal recommendations helped. The problem disappeared when I wrapped the handlebars with fresh bar tape. Not padded or special in any way, just regular cheap as I could find bar tape. It might have been coincidence, but I don't think so.

My theory is the old tape had gotten worn and mashed around so that I had a pressure point at just the wrong spot, or the grip diameter was too small and pressed a nerve or blood vessel, so a new even wrap alleviated it. It's worth a try.