I just replaced the alternator on my '08 4.8i. Symptoms were:
1. Occasional bearing type noise. Stop engine, restart and noise went away.
2. Occasional dead battery and engine stop while driving.

The failure mode was sporadic. Most of the time, it worked fine. But, when it did not, I ended up stranded. Rebuilt (OE) unit from Auto Zone solved the problem.

Normally, I have alternators rebuilt rather than replace, but time was short as I needed to go on a 1200 mile road trip. So, replacement made the most sense. I also suspect the voltage regulator (noise and no sporadic no charge condition) as the bearings felt fine when spinning by hand.