I have a 2002 Suburban with the 5.5 L flex fuel engine (Z) at 140K miles. I am getting no codes and the vehicle runs well. Should I be concerned about the oxygen sensors? The sensors are Denso and appear to be original (I have owned the Suburban since 80K). If I need sensors, should I use the part number stamped on the present sensors or go with the latest shown in the GM parts catalog. The numbers are not the same! There also seems to be some confusion in the parts catalogs concerning the connectors. Some show an in-line 4 pin connector and other catalogs show a 2X2 pin arrangement. For what it's worth, my Suburban was assembled in the Mexico plant.