2003 Chevrolet Silverado

Electrical problem
2003 Chevy Silverado V8 Two Wheel Drive Automatic 135k miles

I recently had to replace my battery in my 03 Silverado and came to find out that my alternator was bad. I confirmed this by taking it in to AutoZone and having it tested, however, after installing the new alternator Iam experiencing the same issues. The truck starts and is fine, when the lights are turned on it dims a little bit but not as much as before same when the fan/ac/heat is turned on. When I put the truck in drive it will draw way down the rpms drop and come just short of dieing. Im not the best at eletrical but do have a basic understanding of it but I seem to be stumped. Thanks for your help.
February 24, 2009.

Take the truck back to Autozone and have them re-check the electrical system (battery, starter, and alternator). Please post your finding along with which Silverado you have (1500, 2500, 3500, HD or not HD), engine size, and the amperage of the alternator that you purchased. Part number to the alternator is enough. I can research it.

Feb 24, 2009.
Hello, autozone can check the charging system. They can also check some codes. I don't know if they can check manufacturer specific codes for the charging system?

I'd use a voltmeter on the alternator bat terminal, take a reading with the engine idling, take another reading at the battery posts, the readings should be real close to the same.

Also the gray wire from the alternator, should be a duty cycle on that circuit, on and off pulse, engine running.

Feb 24, 2009.