Only thing is, on the ground we have NONE of these problems. He woahs, trots, backs, bends, everything. His attitude is completley different. The other thing is that he'll really track up, reach for the contact, and carry himself properly at the walk, but the second I asked for the trot he's hollow out, start pulling on me, and just fall apart. I know it's me not getting something here, but it's not helping that he's figured out just how much stronger he is than me. I really have been trying what you all suggested and have been riding more with my outside rein.
I still want to go back to my first assumption - the Gag Bit is at fault.
While you used the Gag Bit all this time you've been leasing him, and all that time that his previous owner used it on him - he has developed all the incorrect muscles because the bit was doing its' job - creating pressure.
So over all that time, he was never properly balanced because he was never using the proper muscles. And so on and so on and so on.
So now, that you've changed the bit, and aren't using pressure on his front end to get a level of control, you are now realizing - that you have to start back at square one again, to rebuild the proper muscles he needs, to be lighter, softer, balanced and able to carry himself.
The reason why you have it at the walk, and loose it at the canter - is because he doesn't have the proper muscles needed, to withstand the gait.
I do not believe this has anythign to do with him thinking he has one up on you - that isn't how horses think - the reason that he is acting the way he is, is because the Gag Bit muted/hid/camoflauged the all the faults, and now - they are re-surfacing.
So, you have to change your way of riding - to meet half way.
My coach says "If you bake a cake with 1 recepie and the cake turns out to be a failure, you're not going to a second cake with the same recepie, you're going to change it"
Same thing applies. If you have done all you possibly know how - on how to change this outcome, and you still haven't gotten it right, stop and figure out what it is that you could be doing incorrectly in the saddle, that isn't making what you are asking clear to Zeus.
If you can get someone to vid your next ride, and share it with me or Anabel privately in a PM - or Spyder - that would be a great help.