[Excaliber]

Sure sounds like a heat induced problem, this is a head scratcher. When at temp and with the amp reading negative I'd 'by-pass' the regulator to eliminate IT as a variable.

When by-passing (shorting) the WIRES TO the regulator (not the regulator itself) the alternator should put out MAX power, so don't run the test to long. Which wires do you jump to by-pass the regulator? Gotta look it up somewhere, it can also be 'jumped out' at the alternator but it's much harder to get to the wires in that case.