I have a 97 expy with the 5.4 motor it has 137k miles. I have owned it for the last four years and have never replaced the o2 sensors.Its not throwing any codes should I go ahead and replace them or wait for trouble codes. I was hoping to replace the cats and sensors at the same time.

 

If it ain't broke...don't fix it.

 

...and if you have no evidence that they're "broke", then they're probably not broken and should be left alone.

Steve