Updating this saga.
Gypsy has been on the z/d for about five weeks now. The vet originally told me that I should wait six weeks, but I have not seen any change in the hair pulling, but I have seen another problem. The z/d does not agree with her irritable bowel. That is a much bigger problem for us and since I have put her on this food she has pretty much not had a solid bowel since. So I put a call in to the vet today and I'm going to swtich her back to her old food. I think that leaves the hair pulling to stress (or possibly being overweight).
Originally I said I hoped it would be the food, but now I would rather her body run right and the hair come out. Several cat owners have told me that they have had the same problem and that sometimes it goes away. I'm crossing my fingers that this is true, but I know that she will be happy to get back to feeling normal.