Much better off having your PCM flashed. Your most likely going to need it reflashed anyway for gearing,speedo, ect. If your going to use 4T60e/4T65E you'll have to to get the shifts right to match your tire size/gearing. Vats, Passkey1 and Passkey2, The PCM expected a 50/30 hz signal from the BCM or TDM(theft deterent module). You used to be able to install a simple signal generator to supply the PCM the signal expected at the VATS/Passkey wire. Anything after that used a serial data signal that was Vin matched. If communication between the controllers were lost, PCM does not control fuel.If the PCM was replaced it got the last code in the BCM's memory. If the BCM or TDM was replaced it got the last code from the PCM. IF internal memory was reset on both, the serial code had to be reflashed. Later models have to be flashed if any are replaced. If you order a PCM from the dealer they can preflash for your vin code. Being that you will be using an 04 PCM in a swap, you can forget GM flashing it. You will need it flashed. Or buy a passthru/flashable scanner with editing software. Be glad you are not dealing with a late model Chrysler with a "Halo Key". You have to have the PCM flashed when replacing the ignition lock to match the new lock signal. Honda/Acura also. Screwed several times by dealer parts sales stating that the part would be vin matched. We stopped bothering with that hassle and have an independent locksmith reflash for about $125.00 a pop. Cost them around $15,000 a year in software updates to do it legal. Proof of ownership by the customer has to be shown and changes kept on record. Where I work our scanners are capable. However being a national company there are too many legal issues for us to have the software. It would be too easy to be used the wrong way. Sucks being able to see the data menus and having the edit/change options locked out.