Re: please help!!
driving bit is a big no for riding, they are designed to be used with very light signals, not a constant contact.
Instead of going stronger and stronger in his mouth, the issue needs to be addressed and solved, instead of the symptoms. Going stronger and stronger is going to make for a very unhappy horse.
As you have got his teeth checked (well done) next step is to get his back cheacked and saddle checked as well. If he is jumping and curving his back with it being sore, then it is going to give him a big surge of pain, either through nerve troubles or pinching saddle and he is going to try and run away from that. The action of lowering the head may also be very painful for him. Get a good chiropractor out and give him a full assessment to make sure no pain is involved and the saddle is ok.
IF everything is pain free then he needs taking back to basics and starting again in a snaffle. He is just waiting to be pulled and gobbed so he pulls first. He needs to learn that the bit isn't going to hurt and to relax with his tack. Get a nice mild snaffle and start basic lunging and work in a pessoa to teach him about contact when he is comfortable and happy in his mouth then you can start riding again on a loose contact and build it up until he is happy.
I suspect though that he is either associating or experiencing pain whilst ridden and trying to avoid it. If he eats with his head up, the action of lowering his head is probably painful. Strong bits are never the answer. if in doubt, take the bit out and ride bitless in a dr Cooks. Not having anything to associate with his pain might make him respond better.