Since you have a RPO code, what is it??? Take a "clear picture" of your RPO code sheet. Let's see what you got.
Now to the 10 simple steps:
Programming for Pre-2007 GM Models
1. Get inside of your vehicle. It is necessary for you to be near both the inside locks and the ignition. Make sure you are sitting comfortably in your seat, and that the keyless remote is close enough to the steering wheel and locks.
2. Close all the vehicle doors. Make sure that each door is shut tightly, otherwise the vehicle will not sync correctly. If you can, give each door handle a yank from the inside to make sure that they are closed as tight as they can be.
3. Insert the ignition key into the ignition lock cylinder. However, do not turn ignition switch yet. This will screw up the cycle you will have to start over.
4. Press and hold the driver door unlock switch. This is the switch on the door, not the remote. Do not let up on the lock, otherwise it will mess up the process and force you to restart
5. While holding the door lock switch in the unlock position, cycle the ignition ON, OFF, ON, OFF, ON, OFF. Only turn the key as far as it will go before the ignition actually starts the engine. You do not want to start your car. Every time you turn the key to the ON position, a light on the dashboard should appear, and then go away when you turn the key to the OFF position. Do this step quickly.
6. Release the door unlock switch. The doors will lock and unlock one time to confirm the program mode is activated. If the door only locks, or only unlocks, you will have to start the process over again. Something likely went out of sync, or you did not turn the ignition ON/OFF fast enough.
7. Simultaneously press and hold the lock button and the unlock button on the keyless remote for fifteen seconds. The doors will lock and unlock as you are holding down both buttons to confirm the programming of that transmitter. Do not wait to do this step. You want to do this within ten to twenty seconds after you have shifted the ignition ON/OFF.
8. Repeat the previous step to program up to four transmitters. Once more, do not wait very long in between transmitters. Otherwise you will lose the sync with your car and have to start the process all over again.
9. Turn the ignition switch to the ON (one more click forward) position in order to exit the keyless entry transmitter mode. If you forget to do this step, it is likely that your car will not unlock/lock properly.
10. Operate the transmitter functions in order to verify correct system operation. Step out of your car, and go as far as 20 feet. Test the locking mechanism on the transmitter. If it works from that distance, step back another 20 feet (40 feet in total) and try it from there. If you are noticing it not working, you may have to restart the sync cycle over again. It may also indicate the battery is low.