Hello everyone. I am having a problem with getting my egg up to temp. It has been taking longer and longer get to even reasonable temps like 400. Today it took about 20 minutes to get to 400 with the vents wide open. I am cooking duck on v rack with drip pan direct. Put my pan in when temp got to 400 expecting it to go down and come back up. It went down to 300 and 45 minutes later just got back to 400. Any ideas about what is happening? Before this cook, really scraped out the lump to get any ash down into the bottom and cleaned out ash to make sure good airflow. Added new charcoal to top of box before lighting.