This tip might be more helpful for expectant purchasers of a new barbecue pit (as opposed to a gas grill). If you have had difficulties controlling the heat in certain cookers, take a look and consider the thickness of the metal that the pit is made of. A pit with thicker sides (up to 1/4 inch or more) are easier to maintain the heat. They take a little longer to reach operating temperatures, but once there, they maintain the heat more consistently. If your pit is made of the thinner metals (such as in the Weber kettle) then, when the heat dies down, so does the internal temperature inside of that pit because the metal quickly begins to cool. This leave little expectation of regaining normal cooking temperatures easily. When you have a choice, go with the thicker metals for your new barbecue pit.
Enjoy!