Hi. I'm new to this forum. I'm showing a PO155 code on my 2003 S-10, 4.3, 2wd. I'm planning on changing it tomorrow and a friend suggested to change both of the sensors that are upstream. Anyone have any experience on this? Aside from this code, my truck looks and runs as it did when I bought it new. It now has just a tad over 162,000 miles on it.