I think Vinh is right. I do not think your PCM is bad and your 12v signal is very weak. Just try as stated to "hot wire" everything right to the battery. You should get the engine to start that way. Took me, Vinh, and John at Speartech to figure this out.
Which LS1 motor do you have? I do not have my oil pressure sending unit hooked up and it starts...hope that helps.
Clive