F-150 charging problem

Quick question...

My company vehicle is a 2002 F-150. I have noticed lately that when I have the engine revved high, like kickdown for passing, the battery warning light comes on and the voltage drops (headlights dim, etc.) When the engine comes back to cruising rpms, the alternator/charging system acts normal.

In older cars I know the alternator had slip rings, but I think the newer alternators are rotating rectifier assemblies. Anyone had this problem before?? I would assume that if I replace the alternator, it will take care of the problem.

The truck has the 4.6 liter engine.

I got one of these on ebay a couple years ago for my 98 F-150

http://cgi.ebay.com/ebaymotors/New-MotorCraft-130-Amp-Alternator-Ford-Truck-E-350-Van_W0QQcmdZViewItemQQcategoryZ33573QQitemZ8021174 635QQrdZ1

it my be a bad alternater, or a battery(it is a slim chance) but if either of the two are bad then when your engine reves up they dont have the energy to keep every thing running at optimum performance and provide power for the additional spark(you probaly already know but for those sho dont) when you accelerate your spark plugs fire more and use more power and doesnt allow the battery to regain the power untill you go back to cruising rpm. but i think it sounds more like the alternater. i hope that helps you.

There is a "WOT cut-out" relay for the Alt and A/C compressor to give all the available power to the rear wheels at full throttle.

I would not concern myself with that light if only at WOT.