From the 04 manual;
P2096-DOWN STREAM FUEL TRIM LEAN BANK 1
When Monitored: With the engine running in closed loop mode, the ambient/battery temperature above (-7°C)20°F, altitude below 8500 ft and fuel level greater than 15%.
Set Condition: If the PCM multiplies short term compensation by long term adaptive and a certain percentage is exceeded for two trips, a freeze frame is stored, the MIL illuminates and a trouble code is stored. Two Trip Fault. Three good trips to turn off the MIL.
There is one sensor before the cat and one after.
If the cutout is before the rear sensor, that is the problem.
Or, there is a problem with the rear sensor, like it was overheated with the install of the cutout or something.
The code is saying that there is a problem with the rear sensor readings.
If you are routing the exhaust out before the rear cat, that sensor cannot detect the correct mixture.
If the sensor was burnt out with welding heat, then that is the problem.
Don't know about 05's, but that is the case with the 04's.
Another thought, if you can't find a sensor at the rear of the cat, maybe the insaller removed and that is your problem.
That is why you got to learn to do this kind of stuff yourself.