I've been following this thread since the beginning because I am considering a Safe in the future. The one thing that stands out to me is you trying to heat 5 gal of water and expect your temps to stay at 275, and your chewing through the lump at a high rate. Your using all the BTUs from a small fire to heat 5 gal of water. This is like putting a large stock pot on the cook top filled with water and putting the burner on med low and wondering why it wont boil to cook your pasta. I've watched the Video on the Pitmaker site, the pan is dry the exhaust is full open, the intake is barely cracked open and it is running at 255. This pit is just a super efficient UDS because of the insulation. I think you problem is fire management.
Fill the basket with charcoal and drop in a few chunks of wood remove a hand full of charcoal from the left rear corner of the basket( the furtherest from the intake) light this in a chimney and drop it back in the empty space close the door and open the intake and exhaust all the way when the temp gets to 175 close it 1/2 way, when the temp hits 230 close it to 3/4 closed at 250 close it to 1/8 open. Run the pan empty, once it settles in adjust the intake to your cooking temp.
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