How many miles on your truck? and what engine. The 3.0 and 4.4 have a couple different situations that happen to cause a Alternator failure. Generally the Alternators go for a very long time on the 3.0 engines if you keep ATF out of them from the power steering that is filled right above the alternator. Changing out the brushes/voltage regulator is usually all that is needed on a high mile unit, unless it’s squeaking.

The 4.4 does seem to suffer from earlier than expected Alternator failure (IMO). I think using that MEGA expensive water cooled alternator did not produce the same reliability as a standard air cooled unit.