Found the answer. Pin B on the lsx 4 pin alternator connector should be connected to red pcm connector pin 15. I had this wire connected to battery voltage. Out of pcm R15, this voltage is about 9 volts. Not for sure, but this is probably why i was burning up alternators, too much voltage on this wire. some pcms have two wires, another going to R75 and pin "C".
Steve
66 Chevelle, 454, 200r4, 12.9's, 86 K5 with 5.3