I was cooking a prime rib yesterday and started it at 500 degrees to get the exterior nice and brown, but when I tried to reduce the temperature to 275 for the rest of the cooking time, I couldn't do it! I completely shut the dampers, I tired setting the dampers where I usually set them for 275 and waited 15 minutes, but it only dropped to about 400-425. I tried shutting the bottom and opening the top to let the heat out, and everything in between, but the egg wouldn't go below 375. I gave up and put the roast in the oven in defeat. How should I have done this? Thanks!