Good info, some of which is new to me, personally.

But a lot of it may well not apply to the OPs '01 5.9.

And I would still weigh the costs vs the benefits before I spent the time and money to change the down stream(s) on this vehicle unless there was a direct indication of a problem with it.

So where does that leave us on the O2s that are universal and require the plug to be spliced on. The Bosch is original on a lot of vehicles and when you buy the replacement, it often needs the particular plug spliced on.