With Graves Disease, the thyroid produces too much thyroid hormone. Levo is given when the thyroid does not produce enough, so apparently, you were hypo before your TT, which means you wouldn't have had Graves Disease. Since you no longer have a thyroid, there's nothing to produce too much hormones except the medication you take on a daily basis, so, no, you can't develop Graves Disease after TT, but you "can" be over medicated.