The 5th plug is a 2 pin plug that is 1 wire in a big loop. It is not usually used on retrofit jobs. I really don't know what it's there for anyway--It is just a big loop of wire. Your 5 plug PCM is a 96 or 97. To the BEST of my knowledge 96 and 97 Black Box Vortec PCMs are not supported by EFILive.

Jeff