How do I find out which Passlock system I have 0n a 1998 2500 GMC

MC on 1998 GMC 2500 Pickup

I have recently changed the cyl&key and the passlock sensor ass.,and will recognize the key, but after a few key cycles, the security light will begin flashing again. It will go out after learn procedure.

Asked by for the 1998 GMC 2500 Pickup