http://lt1swap.com/identify_vortec_engine.htm
The TAC module HAS TO MATCH pcm fairly close. The 99-02 TAC MUST be used with a 99-02 PCM and proper operating system in the PCM, same goes with the 2003+ TAC. I have found the same TAC module was used in the 2003 to 2005 pickups. 2006 The TAC module part# changed, and was used with a different gas pedal as well. The 2006 gas pedal harness will have a large 10 position connector on one end (6 pins used) and a smaller 6 position connector on the gas pedal end. The 2006-07 TAC module must be used with a PCM programmed for proper 2006-07 operating system. There is an 8 digit number below the barcode of the 2003+ TAC module.
2003-2005 TAC # 12573058, 12588923 <= should both be compatible for 03-05 pcm's. I have used the 12573058 all 3 years no problems, not sure on the 12588923.
2006-2007 TAC # 12590008