Charging problem on 99 3.8 camaro

We have had the battery checked it is good
We have had the alternator checked it is good.
All the fuses are good.
What can be or is the problem.

Is it not charging at all? If all the parts is good and its not charging still, check the power to the alt, and use a multimeter at the battery and make sure the charge is reaching the battery. If the alt is putting out 14.4 volts, and your only reading 13.8 at the battery, you have a problem for example.

You will have to talk to some of the 4th gen guys on this site tho, not sure but if i remeber right the prob could be the ECM?