HiCustomer welcome to Just Answer!.
Check this for me first if you would. Start the engine and check the two small studs on the back side of the alternator
for voltage. These are the field control terminals, BOTH of which will have equal voltage if the PCM has lost its ability to regulate the charging system.
If you have only one source, check to see if the side with NO voltage has continuity to battery
negative. A good method for this is to use a 12v test light connected to battey positive. If it lights when touched to the dead terminal, the PCM is OK and the alternator is at fault.
I can describe a way to add an external regulator, but there's a very good chance that you'd have to live with an always-on CHECK ENGINE lamp from that time on.
Speaking of CHECK ENGINE lamps, it might be worth checking codes before we get too far. You can have the engine scanned or use the "flash code" method, something built into the truck's electronics. Here's how it works...
Roll the key from off to on three times, leaving the key ON.
Watch the CHECK ENGINE lamp as it does a longer than normal bulb check (close to 5 seconds) and then goes dark.
When the CE light comes back, it will be flashing, so be ready to keep count.
The pauses between flashes tell you what to do. Short pauses mean you should continue counting... this digit isn't done yet.
Longer pauses mean the digit is completed and you're moving on to the next one.
All trouble codes are composed of two digits, like 12 or 55, so you will always have an even number of digits once the flash code process is over.
Repeating the process 2-3 times is highly recommended if you're not a flash code veteran... codes such as 12 often become... "3" if the pauses aren't recognized.
Let's see if there's something we can use in there, but if the battery has been disconnected or gone dead codes may be lost... that's what a code 12 indicates, recent loss of memory by the way, with 41 being a charging system code.
Check these few things out and we'll move on from there.