Voltage drop at 1800+ RPM???

[66sprint6]

On the way home from work today I got on the gas a bit in 1st and noticed my battery light come on. Let off the gas and it went away. Noticed it turn on and off as I was driving, almost as if it were a shift light and the voltage on the stock gauge drop. After a bitof messin with it, realized it would happen right about 1800RPM and would turn off as soon as it dropped past it. Itll do it free reving as well. I took the neg cable off the battery and the car ran fine, reved it and she dies. Only thing I can think of thats RPM related i the electrical system is the ALT so I took it off and let oreilly's check it out. It passed...grrr....what the heck? Car didnt run any different, sound system was goin at the time and it kept bumpin...any ideas? The guys at Oreillys said to check out the wiring and if it keeps up they will give me another ALT to try out. Hope this is nothin big but its puzzlin me so I thought Ide send it yalls way.
Thanks!
Matt

 

[HISSIN50]

Don't pull the neg cable off a computerized car that's running.

I would try to test the A, S, I and rectifier values while the battery light is on (being careful of moving parts, hot parts, etc).

 

[66sprint6]

battery light only comes on over 1800 RPM. From 1700 and down it turns off and the gauge returns to normal. Im still not convinced the alt is in perfect health, hopefully i can dig up another 3g to test.
Matt

 

[HISSIN50]

Since it's a LLT 3G, I'd just swap it in. The reg might have taken a dump (if you have a spare reg, it's 2 mins to swap regs).