I'm going to disagree with both post 2 and 4.
Going back to another throttle body just seems counter productive, but with the lager TB getting a "tune" is a good idea. I do not know if it is necessary. Rob at Needswings could give you a definitive answer so I would telephone him. The CAI is not the answer to your problem.
Code P0123 Is set by the Accelerator Pedal Position Sensor. (your foot pedal). It indicates a short to voltage, a sensor ground open or possible a problem with the PCM. This code will cause acceleration rate and engine output limits. You are correct to start with replacement of your foot peddle. There are test procedures, but they require a DRB III to make it simple. Curled up under the dash is not fun, so I would just get a new APP sensor. However I would be certain all the connectors are clean. If you see corrosion you may be able to clean the connector and make it function. Good Luck!