when the engine is hot, what is the battery voltage at idle?
when hot - does the battery voltage increase when you rev it above idle.
an alternator i had was too close to the exhaust manifold and the internal regulator was getting overheated when the engine had been on boost for a while - if this is the situation in your case then exchanging the alternator would yield the same result
I'll check this but if I remember it was more than showed me the IAW-monitor connected to the ECU. It was slightly above 14V.
And the problem with drops during the boost then already was.