Low Voltage

I have a 97` Z71 4x4 w/350. Last Year the Alt went bad so I put a new one in and a battery to.No big deal.The problem is everytime the motor hits about 4200 rpms or so,the battery light comes on and the lights dim
very low and the volt gauge drops way down until it shifts.It didn`t do this before. I have changed the alt now 3 times from different places and still the same thing happens. I have taken it to my shop and everything seems to be charging fine. I have checked all the wiring and the grounds to. What`s next?
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If all is charging correctly and the grounds are all good, then possibly there is an engine RPM related issue with the ignition or computer system?

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I`ve had the truck on the scope,and nothing was found. Wouldn`t I get a serive engine light?
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belt slipping at higher RPM ???

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New belt
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tightened properly ?
good finish on pulley ?
tensioner in good shape ?

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I have checked all of that a few times. I have been ignoring it for a long time. Should I just not worry about it until it causes more of a problem?
1/4 Mile Junkies
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Possibly not, there could be some component using a high amount of current when the motor is at 4500 rpm. I couldn't say what. Did they put a load test on the alternator when they tested it? And did they run it up to 4500 rpm when they check the charging system?

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Bill S wrote:

My girlfriends car was doing the exact same thing... We thought.
Turns out it was the low-coolant light the whole time. Not the battery light. Doh.
Every time she'd accelerate hard, the coolant would be pulled to the back of the tank, tripping the light.
-marc
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