If you haven't already you can check out the heater meter forum. You can learn a lot about ATC there. My first guess would be Ash buildup began affecting your cooker after a few hours. And your temperature fell off. A controller will help with that because it can boost the air flow to keep powering through that.... The temperature does get a little squirrely when it gets to a certain point. Helps to have more coals available.Thanks for the feedback everyone! I stumbled on the existence of these temperature control devices after having yet another long cook go awry. Latest… woke up to my overnight pork butt smoke with the grill temp at 170. I’m sure more practice will help. But i’m also open to the shortcut method.