Okay I need help quickly. Fuel tank on my 07 is holding pressure until I unscrew the fuel cap. I recently had the head off for new head gasket. Wasn't holding pressure before the new head gasket. Iv tried cleaning the tank vent. Still holds pressure. Truck has 250 hp nozzles, twin CP3, and an air dog 2 165gpm. I don't know what else to do or to check. Any help is greatly appreciated at this time.