99 Chevy Silverado, 5.3, z71. Trouble codes p0138 and p0141. It was in same 02 Sensor, Bank 1 Sensor 2. I replaced 02 Sensor behind cat on driver side. The codes kicked back. Whats should I do? I really appreciate any help. Thanks.
Bryan

 

http://www.obd-codes.com/p0141

http://www.obd-codes.com/p0138

and i'd replace fuel tank cap and run can of seafoam through tankful.

 

fuel cap won't do anything to help the problem.
If you have already replaced the sensor, and you are geting the exact same codes back, i'd be looking into the wiring leading to the pcm. May have a few chaffed wires causing the problems