1984 Trans Am Charging Problem

I got a strange problem that I have not been able to figure out. It is a 1984 Trans Am with a 5.0 in it.

:banghead: When the car is at idle I get 14.2 volts and everything works fine. Once you come off idle the voltage starts to drop slowly and it gets down to 11.1 then it stays there untill you get back to idle then it is fine again.

I have replace the alt., Battery and Battery cables. I not to sure where to go next.

I'm assuming these readings are off the dash gauge. Have you rverified this anomolly with a voltmeter on the battery? Otherwsie I would say poor belt tension.

The readings were taking with a volt meter at the battery and the alt.

Not that it should matter, but since it's a T/A, is it cross-fire injected?

I only as cuz the only other possibilty here would be a binding pulley or a possibly a bum fan clutch putting extra strain on the water pump bearing?

yes it is cross-fire