4 Alternators in 6 months due to the voltage regulator failing. They have come from 4 separate sources, including Ford. Both batteries are just a year old and have been tested for problems or bad cells – no problem.
Are you jumping people off or getting yourself jumped off?
Are you disconnecting the batteries before you swap out the alternators?
What is the power rating on that stereo you installed last February?
Each time you replaced the alternator, did you charge the battery before restarting the truck?
When you shut off your truck the battery is well charged. So it is easy for the alternator to replace the little power it takes to restart the truck next time.
This may be what happens.
The original Alternator dies, Battery is drained below it’s capacity to run the truck, That’s when you knew the alternator was not charging.
You replace alternator and Jump the truck because the battery is still dead.
The high load put on the new alternator burns out the voltage regulator in the new alternator.
Then you go through the same thing again and again.