Had a 6600 without filler plates that developed a gradual tendency over a two year period to plug up in high residue crops like beans and wheat. Especially if the stems were a little tough. Found two notable items: First, the cylinder speed range recommended by JD is appropriate. However, if the crop residue is heavy and_or tough it is difficult to maximize combine capacity if you start on the lower end of the range first. Instead, start at the higher end of the recommended cylinder speed range, find your maximum ground speed and then reduce the cylinder speed till you minimize the grain damage to an acceptable level. Second, we found most of the cylinder plugging that we were experiencing to have occurred as a result of the beater having slowed or stopped turning. Upon closer inspection we found both pulleys on the beater drive worn to the extent that even a new belt would slip. We replaced the pulleys, disassembled and cleaned the tensioner pulley arm. After that and another new belt we had an eating machine. Running a 7720 II these days. It has filler plates and they are not removed for any crops.