1997 Sierra K1500 project help

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Dirtguy

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Hello, my name is Eric and I live in Colorado. I’m currently helping my son fix up a 1997 GMC K1500. We have replaced the engine with a long block re-man 5.7 Vortec, we replaced the starter, alternator and Battery.

We have a parasitic battery draw that we cannot find. We removed the alternator and took it back to parts store for testing and it tested fine. The crazy thing is that he will drive the truck 2 days and then needs a jump to start, but if we charge the battery and let it sit un-driven for a week the truck still starts fine. Pulling my hair out by now and hoping this community can help. Thanks for any and all help or guidance.
 

Dirtguy

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Ok, alternator has now been replaced again with a new one not a re-man. Still no charging. Volts sit at 12.5 or so when off and drop to 12.05 when started. This is both at the battery and the back of the alternator when engine running. So the cable from alternator to battery is good since it reads same voltage both places. Why won’t the alternator make energy? Is this a PCM issue?
 
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