How did you measure your temperatures?
If your controller was set to 225F and the actual temperature was only 200F, you would not have enough heat to properly break down all the fat and connective tissue in the pork butt.
I love pulled pork. I typically cook butts at 225F as measure by a 3rd party thermometer until they reach 165F as measured by a 3rd party thermometer. Then I wrap the buffs in foil adding some butter and a mixture of water, apple cider vinegar and apple juice, but any liquid can be used. I turn the cook temperature up to 275F as measured by a 3rd party thermometer. The liquid allows the pork to steam inside the foil. I will allow the butt to cook until the temperature reaches between 200F - 205F. Remove the butt from the grill and allow it to rest wrapped in foil until it is cool enough to pull. You should find the pork to be tender.
If you still have the tough pork butt, place it in a crock pot with a little liquid and allow it to cook on high until tender. If you do not have crock pot, you can accomplish the same thing in a dutch oven or covered stew pot.