I'm doing a butt and I was doing alright, not fantastic, but pretty good with holding the temp. Then about 3 hours in the pit temp started to take off. I closed all the vents except the top vent and nothing was helping. I had a heck of a time bringing it back down. What would cause this. Any tips on keeping the temps down. It seems to run a bit hotter than I would like with little to no bottom vents open. I am using a terra cotta diffuser and for this cook I have at the steamer ridge level because there was too much fuel for it to sit on the bottom like I intended to do.