I have a 2002 LB7, with 4" exhaust. I have now installed a aem "Brute Force" intake system #21-8013dp. The filter restriction gauge now shows full restriction all the time. I reset it and stomp on the pedal it's back to full restriction. I called aem and they said because the velocity of air is now so great that there is a negative pressure being developed and that's what's causing the gauge to show a restriction instead of there being an actual filter restriction.
True??