On a side note, if the fan fails, you can get a Ford motor + pigtail harness for the fan assembly. New 5.9 fans are hard to come by, factory does not sell just the motor, and a new fan assembly these usually costs in the region of 700-800$. New Ford motor (which is the exact same unit, with slightly different connector) with the pigtail is around 100$ shipped.
This just to let you know when the fan fails. It's usually the slow speed that dies first.
Mine runs for a certain time after I turn off the truck. Let it run and if it doesn't kick off after 10 minutes or so you know you have a problem. As a matter of fact, with the car now off and cool, put the fuse back in. If it kicks on, chances are your relay is shot.