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The code P0603 refers to no keep alive power to the PCM.This can be set by a faulty PCM or by power interuption to the PCM.Given that the truck doesn't start,I suggest checking for power to the PCM.
Note: This code may have been caused by disconnecting the PCM or the batteries.
Was DTC P0603 present?
Is battery voltage present on both sides of the fuse?
Is B+ present?