The dreaded P0171 code

I know this subjuct has been discussed ad nauseum, but my 2000 Taco (V6, auto, 4wd, ~170k miles) the much dreaded P0171 code.

It is always P0171, I have never seen any other code. This started about 6 weeks ago.

So far, I have changed the air filter and the fuel filter, cleaned the MAF and ran about 5 bottles of fuel injector cleaner through the system.

I was watching the voltages on the O2 sensors using Torque (pretty cool app, by the way) and the #2 O2 sensor just intermittently flat-lines. It will drop to about 0.1 volts for about 5 seconds, and then it comes alive again. While it is dead, I can see the voltage on the #1 O2 sensor start to climb. When it hits about 0.8 volts, the code is thrown.

The #2 O2 sensor is the after the Cat, correct?

I don't mind spending the $60 on a new sensor and installing it if that is really the fault, but in reading the other posts on these codes, it seems like it is more of a hit or miss sort of thing. Can anyone recommend further troubleshooting to give me more confidence that the sensor is really bad?

I'd like to pin this down quickly because in early Spetember, the truck is due for the emission test and if they see the code during the check, then I have to have the repair performed by an "emission certified" repair facility. I don't even want to guess how much they will soak me for this.

Thank you in advance.