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Sounds like either a belt issue or battery/alternator issue. If you go to sears they can run a full battery/charging/starting system test on the vehicle.
i would check my power steering pump also. if you dont have power steering the pump could be going out and seizing up the pulley which would cause drag and not turn your alt pulley fast enough.
Sidenote, should your pulley tensioner assembly move AT ALL during idle? I noticed a squeeling pulley on my startup the other morning and noticed the tensioner just kinda moving a tad back and forth during idle.