My uncle has an 04 LLY that is having issues. He leaves it idling for 10-15 minutes and then when he goes to leave it kind of bogs down. He said it acts like a gas motor that is flooding. The pedal doesn't seem to do anything so if he holds it to the floor for about 10 seconds it will rev up again. Truck has a Hypertech tuner and exhaust. Anyone have any ideas?