Charging issues
 

Hi all, looking for some help before I go through the 100 step shop book diags.
This is the situation...
2006 Caddy STS 4.9 V8 160000 miles or so.
Cars been great...until... alternator died.
When the alternator went bad I could put the volts up on the DIC and watch as they dropped on my way home from work.
Bought a new autozone alternator and installed.
After the installation, the car shows that the alternator is charging because the volts on the DC climb to 14.5 or o and stay there.
even so, the car is still squawking that the charging system needs repair and that the battery isn't charging. Drove the car for a week like this. Battery is always at 11.8 volts after
an overnight sit.
Ordered a GM alt and installed.
SAME ISSUE! The car starts strong, battery seems to be fine but haven't had it tested as of yet. an 11.8 volt reading on the battery after sitting all night seems to be normal.
Checked the alternator plug and hot wire, all tight. Belts tight.
one thing I did notice is that when I get on it and run about 3000 rpm plus, the battery light goes out for a few but then when the rpms drop it goes right back to the way it was.
Really annoying because it goes into power saver and I cant use my rear window defroster.

Any suggestions? Anyone experience this and actually find a solution?

Everything prior to the alt ****ting the bed was good.

Thanks in advance!

Rob D.