I totally agree with Bigmista. Leave the holes on the top open fully while you cook. You need good convection flow in the drum. I have 3 -7/8" holes on the bottom of my drums. I usually only need one plug out to maintain a temp of 260 degrees. Two out and it goes over 340! I have never run with three out. I use Royal Oak Lump charcoal. It burns quite hot. Brickettes burn much cooler and are very constant in temperature. (easier to control) You MUST light the charcoal from the TOP. If you start it from the bottom you will never be able to control the temperature.
Bill Napper. Team Cook "JoeJo's BBQ"
Custom offset stickburner
Gas assisted cabinet smoker (400 lb. capacity!)
55 gal. drum smokers galore! (All custom built)