Electrical - Voltage Drop

Hey guys, got a bit of an issue thats plaguing me.

2000 Silverado 4x4, 5.3.

My output voltage drops at random. I can nearly always make it happen by "coming onto 'er", getting her to drop a gear/2 on teh highway, revving high. Voltage drops to battery voltage, as if the alternator is no longer putting out power. Sometimes at random just cruising at 1900 RPM it does the same. Battery light comes on if it lasts more than a second (never lasts more than 2-3 seconds), and a code is stored .. . . .dont recall the number off hand, but it's Alternator L voltage drops. something like that. Tried a different battery, same thing. Pulled the alternator, had it tested at crappy tire, they said it's fine. Changed the belt (thought it might be slippling), same thing. All the pulleys seem good, nothing rough, tensioner seems fine, belt is nice and taut. Cleaned up all the wiring/terminals/grounds. Cant seem to find this problem. I kinda wanna believe its the alternator, but I've never seen one go like this. Any ideas?

Evan

tough cookie, I would take the alt to autozone and let them test it, how often does it do this? everyday, if so I would try to replace the alt cause if this goes out your dead in the water. Something could be loose inside of it and when they tested it at the tire shop it was just working normal there

Check the plug on the side of the alt. Start the truck have some one help you, watch the guage and the other person wiggle the wires going in the the regulator on the alt. If that causes the problem then there is a short in the plug or the wires. Seen this same problem on a 99.

Yea, i've played with that plug on the top of the alt a pile already, that was kinda my first thuoght. However, no luck. I guess i'll pop the alt off again, and take it to a few different places to get it tested.