Joan, over supplementation of thyroid hormone would not have a direct effect on lowering cortisol per se; however, hyperthyroidism can put a lot of stress on the body so Gabel may not have had much cortisol in reserve to respond to that stress. The good news is your vet seems to have it figured out. The triglycerides were most likely elevated due to a recent meal so all in all, things look pretty darn good.