It's possible, depending on the load that is being exerted by the electrical components the alternator may be picking up the slack.

 

Anyone want to buy an 03 super crew?

 

like rcairbear said. it sounds like you have a intermittent short. I would check the grounds both from the battery to the chasis and from the block to the chasis. Make sure they are tight and take a wire wheel and clean any rust.

or it is caused by corrosion inside the cable. old inferior grade copper will corrode. if you find the is the problem or if you just want to rule it out, you could go to your local car audio shop and get some 4 guage OFC wire. if you make sure you get quality OFC you wont ever have that corrosion problem again.

also I would not trust the battery tester 100%. it is probably correct, but if the battery is under warranty get them to change it out. if they said something got stuck open and it has to be charged then you should be able to argue it is flawed and get another one.

 

If I lived closer to you I would take it off your hands. This shouldn't be a terrible fix. When you find it you will have to shake your head.

 

do you have skid plates on it? if so you want to part?

Edit: could also be a short in the factory amp. My wife had a 97 mustang where the battery would be dead sometimes and sometimes it wouldnt. and it had all kinds of wierd electrical issues. turned out factory amp was going bad and causing wierd drains on the battery.

 

Fwiw- i had an 07 grand cherokee- it started but ran like crap- the digital message center went bat sh•• crazy!- took it straight to a-zone- low voltage- 10.4v on battery- to this day, i do not know how it started!! - anyway,as it has been explained to me in simple terms,when your volts drop, it changes your amp load,the ecm then reads the wrong values and tries to adjust accordingly- maybe oversimplified, but i can understand why that would be-(but im simple anyway!)
That still dont exempt your alternator- if it has a bad diode, change the diode or change the alternator!-
Just a few suggestions!

 

I'm not gonna sale just parts. I don't like this generation truck