Figured I'd give an update since we do all learn from each other. I've been over at guinealynx since a member there had a similar problem. Because of her, I made the choice to put him on methimazole, even though his thyroid kept coming up normal. It worked for about four months on a small dose and he made it to 730 before he began to plummet drastically again. I decided to take him to a hospital in NYC after striking out with both the exotic vet and others, where they redid his bloodwork because she wasn't happy with the results from any of the vets, and sure enough, it finally came up. When I took him in, he was 623 and dropping quick, they changed his dose to 0.15 and today he's now 822, a month after his visit to the hospital. Sadly, I know the medicine won't work forever, and I've accepted that, but it's nice to know the problem was found.
Just to restate, his symptoms were massive weight loss, insane appetite and water consumption, small stools. Now that he's gaining, his stools have become bigger, but his appetite is still crazy. He also had a mass that made him sound like something was stuck in his throat. When he was put on the medicine the first time, it disappeared, as he began to drop again, it resurfaced. Now it's gone again.