I have a 2000 Z24. Recently my serpentine belt stared slipping/squealing. It slips at low idle but high belt load (AC on or high electrical demand). I've replaced the belt twice, the belt tensioner, had the alternator checked twice, had the alternator bearings replaced, checked the heavy wire from the alternator B+ post to the battery and replaced the battery. If I'm at idle with nothing on then it runs fine and alternator output is 14.8V. If I turn on the AC it starts to squeal. If I turn on everything I can (but with AC off) it squeals. When the belt starts to squeal the alternator puts out less than 12.5V. If I rev the engine up to almost 3000rpm then the squealing stops and everything is normal. But when I come down to idle then it begins squealing. It does the same stuff while driving before anyone asks if it only does it while sitting still. I've wire brushed the alternator pulley but not the AC compressor or the harmonic balancer, neither appear loose. The AC compressor is missing 2 bolts that I'm going to put back in soon, but these bolts have been out since like 2009 when I replaced the motor and the squealing problem has only developed in the past couple months. Please remember the belt on this engine only drives the alternator and AC compressor, Auto Zone and the alternator shop kept trying to point out the water pump and P/S pump which aren't driven by the serpentine belt.

Thanks.