Horse riding heavy on the bit. Advice?

He's just being lazy because he realizes the kimberwick makes him carry himself without leaning on you. Just either halt or go on a circle and lift your inside rein sharply and SIT UP. Don't let him pull him down with you. But if he's running off with you like that then go on a small circle until he stops. You can't let him get away with that stuff when he knows what he's supposed to be doing.