I just replaced two 02 sensors (different locations) on my '97 5.0 after the check engine light came on. The local emissions shop showed the error "02 sensor slow response, bank one sensor one" on the OBDII. A parts store guy took a wild stab & sold me the wrong one, but we got it right the 2nd time.
"Bank One" is ALWAYS PASSENGER SIDE, and "Sensor One" is the first sensor below the exhaust manifold. Unfortunately, this one's up on top of the pipe & a nasty one to get at. But it can be done without dropping the pipe or moving anything. Don't forget to ****** the threads generously with a rust penetrant (liquid wrench, etc.) & let it sit for at least half an hour before trying to remove the old one.
Last, you'll need to reset the computer, either by disconnecting the battery for a few seconds, or reset it with an OBDII Scan tool (some code readers have a reset option). Next, complete the OBDII drive cycle which basically means drive it around town for a few minutes & then out on the freeway between 55 & 60 mph for at least 5 minutes. Hope this saves someone else 50 bucks and a few busted knuckles by not replacing the wrong sensor!