Stock. Upgraded would be 53-55mm depending on the level of upgrades. And I'm talking about real upgrades. 52mm will be fine for bolt ons.

 

Stock size, as it comes from factory, is 50mm taper down to 47 or 48 mm. The Fastman, I know, makes them 50mm all the way through (5.2L) and 52mm all the way through (5.9L). As Cereal said, 52mm is plenty big for most of us. Now, if you were going all out, supercharger, different cam, SCT tuner, Edelbrock/Hughes intake manifold, etc. etc., a larger 53-55 mm might work better.

If you email Dan (the Fastman, email link on his website) and tell him what you all have planned for the truck, he'll give you a recommendation.