> Surprised to find the harness for a 4 wire 02 setup on this truck - and
> only using 2.
That's there for the California Emissions package, which uses four O2
sensors (it adds a pre-cat and post-cat to the existing two sensors in each
downpipe).
> anyone experience adding the upstream ones, and is there benefits other
> than losing $100 in sensors?
Why would you want to do that? First, there are no further "upstream"
sensors than the ones you have now - one for each bank of cylinders.
Second, you'd need to re-flash your PCM with the CA Emissions program, which
will cost you some power.