Silverado keeps throwing P0131

[TDPalmer]

My 2004 Silverado with a 5.3 keeps throwing a Oxygen Sensor Low Voltage Bank 1 Sensor 1 code. The truck will run great all work week, and then towards the end it will stutter and act like it is missfiring & buck or just be sluggish on anything past half throttle. When it starts to mess up it will throw P0131 or Oxygen sensor bank 1 and 2 too lean. I can fill the tank up and it will run fine for a while until about 1/2 or 1/4 tank and it will act back up again and sometimes act up even with a full tank.

 

It started doing this after I filled up at a different gas station, I initially suspected water in the gas so I treated it with HEET and Seafoam. After that did not fix it I checked all the spark plug wires to make sure they was not touching my headers and they all seemed fine. The problem kept persisting so I replaced the oxygen sensor that was throwing the code with no dice. I then took the truck to a mechanics shop and they told me 3rd gear on my transmission was going out, which doesn't seem likely as the truck will run normal and it has always shifted fine.

 

I am truly puzzled as to what could cause the truck to run so sluggish.

 

The spark plugs are not even a year old and are AC Delco Rapid Fire

The spark plug wires were bought when the plugs were

I have full length headers, a black bear mail in tune, and a cold air intake, all of which have been on the truck for about a year.

There are no missfire codes

 

I am open to any suggestions to what could be causing this, it is starting to get very frustrating.

[00Silverado4x4]

Just for giggles, I'd see about checking your fuel pressure. May have a failing pump.