Chevrolet Repair: squealing belt, chevy van, serpentine belt

Question
I recently replaced the serpentine belt on my 1993 Chevy van and now the belt is squealing when taking off from a standing stop, this occurs when the a/c is on, I also noticed that the volt gauge will drop when stopped,say at a red light and will climb back to normal when accelerating, when it gets to a certain rpm the squealing stops.
This problem started when I replaced the belt, never done it before, whatcha think, bad alternator?  

Answer
Check the belt tensioner for proper tightness (or replace the tensioner.(be careful)
The fluctuating in the volt gauge could be the voltage regulator.
But not knowing what year, it could be internally built, meaning replacement of the alternator.
Hope this helps.
James