I've got a 12 lb packer and two racks of ribs on, used a full unlit ring and 3/4 of a full chimney lit in a minion, but 90 minutes into the cook I'm still only at 275 at the dome. All vents are open and the door is ajar. Do I need to prepare another chimney? I'm falling farther behind on my first attempt at a high heat brisket and I would like to be able to eat it for dinner tonight.