If the monitoring device ie.. wideband or tailpipe probe are behind the cats(all 4 ) it throws the reading off by .50 roughly because the cats burn up some unburnt fuel. 11.0 would really be 11.5 on the rich side and 13.0 would be 12.5 on the lean side. Gotta keep this in mind. And if you lift the pedal at all then reengage the engine will dump fuel and you will be temp. lean but then it will richen back up as soon as it sees you reengage. These are some complicated *** cars. But once you understand how they work it's all manageable. Temporary leanness on these cars is ok as long is it's not more than 1-3 sec's, I ran 13.1-1 for over 15 minutes on the dyno and not even a nip at the electrodes. Hope this helps some! This is all considering no meth and no nitrous because with either of these you need a much richer environment like 11.0-1. By the way in your case I would gap the plugs at .030 -.035. The wider the gap the leaner the engine, the closer the gap the richer the engine to the point of misfire. The only reason my gap is so close is the nitrous was blowing out my spark. You should not have to go this close.