LB7 injectors suck, when the time hits that they start leaking or name the issue from the list of trouble items it's expensive if the truck is out of warranty on mileage or time. GM extended that repair timeline but I'm not sure how far it goes now. Many LB7 owners have paid bigtime to fix those when they act up. Better search the defect list and read on it a bit in the high spots to see how they give out in different ways. Hope it's just an airleak on filterhead.