alternators,Car battery light on… New battery and alternator but keeps dying

Hello i have 2001 ford expedition. The battery light started flickering suddenly then it went dead. I got the battery tested at autozone the told me it was bad. I purchased a new one. Then i cranked the truck again it came on and the light was on but no longer blinking. Just on. After an hour of driving my truck went dead again. I then was tolf that my alternator was bad. So i purchased a used one at the junk yard. Aaa came out and tested every thing and said both my battery and alternator were fine but my dropped dead again. Can you please tell me what is making my vehicle die?

My car has