I have swapped out a new Alternator, new batteries, fixed some cables but now the NEW battery's (Aux) boiled over and killed them again.

Do you think it IS the PCM/ECM computer? Try to change out the (battery to battery) cable?

Any help/direction would be great! About to burn it in place. (Denver)

 

It is more than likely the cable between batteries. The alternator feeds the passenger side battery first. The PCM sensor reads the voltage on the drivers side. If there is a bad connection/cable between the two batteries, the PCM will tell the alternator to keep charging and fry the passenger side battery.