This subject seems to be coming up consistently so I thought I'd share this picture. When I bought my truck it had the filter on the left in it.



The filter on the left is an "also fit" filter. Like the rest of the aftermarket folks, except for Fram, the deminsions are not a good fit in your 6.0. The filter on the right is a Motorcraft, With the proper Ford plastic cap. If you are new to 6.0's, take a look and make sure you have the right filter on your truck. An even worse condition is to have the aftermarket (tall) cap with the correct filter under it.

Here is a video with good info. It is promotional so bear through the beginning sales pitch, theres good tech data further in.

Richmond Ford MotorCraft 6.0L Filter - YouTube