I did a quick search, saw different results. My truck has 108,000 hard miles.
The cats were replaced at 65,000 miles by the dealer. However the oxygen sensors are original .

My truck is a 1999 Silverado Z-71 5.3, Auto with basic mods. Cold AIr intake, exhaust, 02 computer, 02 injectors, and Finish Line Level 5 tranny.
Tuning by allen nelson, but before he started, it ran a year or so with hypertech.

My mileage has dropped, plugs look great. Wires are good.

What oxygen sensor is everyone using, and do I need to replace all of them ?

Thanks,

Brian