Hello Sierra, actually I think that a stronger bit only makes the horse get stronger, if you horse pulls you need to figure out the problem.
Can it be a health issue ? Does he have too much energy?
Once you figured out what's wrong you can begin to think about what can be done.
I would advice you to make him lose his excess of energy before you ride him, you can try to lunge him for example ?
Maybe you'll need to take your horse back to the basics, try easy exercises to keep your horse focused, ride circles, loops and other simple patterns. All these schooling exercises can help you to develop a better obedience.
I hope it's helping :)