I have a 1999 Durango 4x4 with the 5.9, my check engine light has been on since I bought it, I originally have a P0132 and P0138 on bank 1 sensor 2. I also had a P0308 misfire on the 8th cylinder. I replaced all of my spark plugs and the misfire went away. I checked the bank 1 sensor 2 with my multi-meter and I just assumed that it was working but I may have a bad cat. So I did the non fouler mod to the sensor after the cat. The check engine light went away for a day to work approximately 28 miles. The next morning about 5 miles into the drive the check engine light came on again. Now I am getting P0132 and Po135 on bank 1 sensor 1. I am unsure why but I was hoping someone on here would know a little more than I do. Do I just need to replace the O2 sensor on bank 1 sensor 1 or have I done something with the O2 sensors by adding the non fouler to the sensor after the cat? This is my first post and I am a noob so please if you can help I would greatly appreciate it.