Alternator or Electrical Issue?

I have the original alternator (95 V6, 190K miles) recently changed the battery, but if I do not run the truck daily the battery loses its charge, I have had the alternator tested at Auto zone and they say it is good to go, any thoughts?

 

Still could be the battery, a bad battery can do some strange things or may have some drain to discharge over night. Take off the neg. batt cable & put a d c amp meter between that cable & post with the key switch off.
You can see then how much drain you have. If there is drain you can start removing fuses til the drain goes away. Open the door & you'll see how much just 1 light bulb pulls.

 

if you don't have amp meter just leave the battery terminal off and see if the battery still runs down, if it does, the battery is bad, if not then something on the truck is draining the battery, most likely a chaffed wire touching ground such as the starter wire which is the most common thing to cause this.

also are you checking it with a volt meter before starting? because it may be your starter is bad and drawing too much juice instantly draining the battery. my uncles Cadillac did that, one crank of the starter and the battery was nearly dead. its rare but it does happen.

 

Thanks, I thought about disconnecting the battery to confirm that it was not a defective battery, then doing what you said with the fuses. I will also check it with a volt meter and report back

 

If you are draining a fully charged healthy battery overnight clearly you have a high parasitic load. A number of things could be causing it such a leaking diode in the alternator. If you have a DC ammeter, you can put in series with your negative battery cable and start pull fuses of the the power lead from the alternator to isolate the load. A normal parasitic load will be under 200 milliamps.