Why would voltage drop under WOT on a newer chevy fullsize P/U?

[TS6]

I just happened to notice yesterday on my 1997 C1500 chevy work truck that when you get on it, at about 3700 rpm the volt meter gauge really starts dropping fast, it goes to 9 volts before it shifts! It may go lower, but 9 is the lowest the gauge reads. What would cause that? I put a new alternator on a couple years ago, old one crapped out, but I never noticed if it dropped volts at wot too. This can't be good, since its lowering the voltage to the fuel pump and everything too. Might cause a lean condition. Any good ideas out there? Thanks!

 

[Turbo T/A 1543]

My bet is belt slippage. The tensioner could be weak or the belt too long. Sometimes the aftermarket will spec a belt thats a fuzz longer than O.E. Nothing to worry about as far as voltage, as the vehicle sees battery voltage.

 

[BuickMike]

Maybe you should try to put a multi meter to a 12V+ source and see what that reads at WOT. Maybe the problem is just a bad guage / connection.