A couple of things. I have four rib racks for my FEC 100 and have cooked 40 racks about a half-a dozen times and have done many more loads with lesser racks. Two suggestions 1) Rotate your ribs mid-cook. Top to bottom and then spin the racks around to where the front is to the back after the rotation. 2) Also, With heavy loads, it is very important that the grease slide (big ss sheet directly under the bottom rack and above the firepot) is centered between the back of the smoker and the front door. If you push it all the way to the back, it can change the heat flow.