Cadillac did indeed use a cylinder cut off featue on the V8s. I remember distinctly because I was in a GM dealer getting service and I got to read a service bulletin taped to the wall in the office. It said that drivers were experiencing rough ignition in the 4 and 6 cylinder modes. It went on to give directions on how to level this out, but that the idle/run in the 6 mode would continue to be noticeably rougher than in 4 or 8. These could be smoothed out after service adjustments but not the 6. The last line read that, after service "this will be considered normal."
