I just replaced a faulty sensor on my 2004 GMC, and although not all trucks are the same, here is the correct answer for my application and probably most similar vehicles (Tahoe, Sierra, Yukon, Escalade, etc) with the same drive train 4.3/4.8/5.3l.
The system is setup almost like you would expect:
Bank 1 Sensor 1 - Driver's side, before catalytic converter
Bank 1 Sensor 2 - Driver's side, after catalytic converter
Bank 2 Sensor 1 - Passenger side, before catalytic converter
Bank 2 Sensor 2 - Passenger side, after catalytic converter
I searched around forums to find this answer, but no one was for sure and couldn't find it in their Chilton's or similar manuals. I disconnected each one, used my engine code reader to see which error was thrown after disconnecting them successively, and through process of elimination came up with the above information.
it is screwd into the exhaust somewhere near the converter
Bank 2 is the side of the engine where the #2 spark plug is. On my 99 Silverado it's on the passenger side.
That would be the passenger side of the engine and it will be the first oxygen sensor that's screewed into the exhaust pipe on that side.
behind the converter on left side
Bank 2 is on the passenger side on a Chevy V6 or V8.
It's the sensor after the cat on the passenger side
Bank 1 is the drivers side of the engine and bank 2 is the other side.
Trouble code P0141 means:O2 sensor heater circuit malfunction (Bank 1 Sensor 2)
Bank 1 on a Chevy is the drivers side. Sensor 1 is located in front of the catalytic convertor and sensor 2 is after the converter. Each side has 2 O2 sensors.
Bank 1 is the drivers side of the engine. #1 o2 sensor will be the first sensor that is in the exhaust pipe that's closest to the exhaust manifold on drivers side head.
drivers side second one back by transmission
Bank 1 is the exhaust pipe on the drivers side of the engine, and the other side is bank 2