But when does it stall? Does it stall when you first start it or after its been running a while? You need to start observing what's happening as it stalls: battery voltage, what's running in the car and what's not (headlights, heater, etc), what you were doing at the time (parked at a red light, hauling on the freeway), and so on. Simply knowing that it stalls is useless to us.

How big is the stereo in your trunk? Could that be sucking more power from your batter/alternator then they can supply? Most kids on this board have $3000 cars and $8000 stereos hence I ask.

The typical operating voltage for a car is 13.8 to 14.4vdc.

If you want to test the alternator, start the car then remove one of the cables from the battery. If the car still runs, alternator is at least semi-good.

To test the battery, disconnect it completely from the car then put a voltage meter on it. Should read 12.8vdc.