Review on Reliable Alternator Replacement for Ford F Series Truck 4.6L/5.4L (97-02), Expedition - 321-1772, 334-2274, F75U-10300-CA/CB by Brad Jeffress

While that doesn't indicate it's under warranty I could buy two or three of these for the price of one with warranty from your local parts store. I was in a situation where I had to supply an alternator and it worked out fine. Installed a few weeks ago, no problems. So far this has worked great and made a huge difference!