T-56SLPSS

I have a 00 m6 with a 6.0 cammed. Having voltage problems. At first voltage was unstable bouncing all around. Now voltage won't hold, especially at night when lights are on. 2 batterys and two alternaters later same problem. Grounded alernater to battery. Unpluged positive to test alternator. Checked red wire and plug off alternater. Still alt won't charge battery. Codes are/ p1546 a/c clutch status circuit low, p0801 reverse inhibit control circuit malfunction, p0645 unknown(a/c?) And p0803 skip shift solenoid control circuit. Help if you can.
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