first thing i would check is the voltages on your alternator both off and when the veh is running. GM alternators are usually three wires. One heavy red wire lugged to the rear of the alternator is the output line. Should read battery voltage 12v +/- 1 volt with car off. On the side of the alternator is a 2 prong plug. Again, a heavy but not as heavy red wire is on this plug as well. Should also read same as heavy red wire on rear of alternator. Assuming it does,, check your idot lite on the dash.. Does that come on when u turn the key? That bulb is in series with the light guage brown wire next to the red wire in the plug. With the key on.. you should have voltage at that line as well.
With engine started, what do you read for voltage accross the battery terminals? IF charging system works,, should be approx 13.8-14.6 volts. IF it is less than that,, you have a problem with the charging ckt and u should start by checking as i described.