I'm not a big fan of Tom Thumbs anyways, but I can say that if your horse is not giving his head willingly you shouldnt be using a shanked bit.
Try going back to the snaffles and get his head flexed well every time you ride. Bring him right up under himself and keep him moving. Just feel him out and give his mouth some space when he shows that he's ready to start listening better.
After you master that, you can try shanks again.