Yikes - you mean the last set only lasted 2 years? How many miles was that? On a side note, someone else with a 606 had a similar problem (short plug life), and was trying to figure out why. He had his injectors tested and found that the spray patterns were poor, which may have caused carbon buildup, which could reduce plug life significantly. You might want to have your injectors looked at, or you could end up going through this whole procedure again in 2 years...