I know I'm gonna rufle some feathers here and I understand that everyone has an opinion and is welcome to it, but, let's deal in facts. The factory GM airbox that comes on every 5.3 and 6.0 liter motor has the capability to flow more air than the engine can use. Even with forced air induction. That's the airbox. The tube that runs from the airbox to the plenum is the only restriction to the design. The restriction lies in the 90 degree bend in the tube. It reduces the inner diameter enough to cause a restriction. Enlarging this area and reducing the drag in this bend is the only way to increase stock air flow. There are a few specialty mfg that have overcome this, but, they almost all use K&N pleated gause filters. When gause or paper filters do their job, that is stop dirt, they get restictive. It is their nature. Only a oiled foam filter will pass close to the same volume of air clean or dirty.
Now, Truflow documents 11 horsepower with their system, and because it uses the factory airbox it is and always will be 50 state emission legal. Period.
Check it out.