Can't get belts to stop slipping

[TorqueEffect]

I've gone through like 3 belts in the last month.

They will not stop slipping, i've tried cleaning the pulleys with a wire brush, different brands of belts (Currently have a Gates belt on there), Tightening it down to the point the pulley bearings make noise, using belt dressing on a new belt.

No matter what I try, belts just keep slipping away making driving embarrassing.

I tested the alternator on the car with a charging system tester at autozone, it passed multiple tests.
Pulled the alternator off and bench tested it, passed multiple tests.

The only thing else I can think of is possibly a very heavy load on the alternator, but I wouldn't even know where to start looking. The slipping/squealing happens on acceleration from a dead stop, and tends to have more frequently, and for longer when there is more high draw electrical systems on. Mainly headlights, radiator fan, and when the a/c is on. But also slips on startup too.

[bravekozak]

Make sure all the pulleys are lined up (using a straight edge).
If it still slips, spray a little belt dressing (tackifier resin in high flash solvent) on the belt contact surface.

[firebush357]

Could it be your A/C compressor going bad?

[WmWatt]

Try cleaning the pulleys with a combination of solvent and steel wool? And check the belt fits the pulley for maximum surface contact.

[skeeters_keeper]

If it just started happening (i.e. nothing else changed right before it began) and it gets worse with current draw, I'd be inclined to think that all the tests aside there is something wrong with your alternator. Bearing going bad, bent rotor shaft, something. Get a new/reman one from some place that will let you return it if it isn't the problem.