The inactive ingredients in Cytomel consist of calcium sulfate, gelatin, starch, stearic acid, sucrose and talc. No microcrystalline filler shown.
You can get Cytomel, or generic, in 5 mcg tablet. That should be a small enough increment for you to titrate your dosage slowly. With that small amount, why would you need to go to a TR version?
Did the hives show up right after you switched?