what could cause a code 304 306. Truck a has a miss runs rough help help help

304 and 306 are both ignition miss codes (cylinder 4 and cylinder 6). Typically this is a secondary ignition problem. If I were an experienced technician, I would swap the coils and the spark plugs to different cylinders and see if the miss followed. If the miss follows to the new cylinder, then you have found the problem. If the miss did not follow then you could be talking internal engine failures, perform a compression test and/or a leak down test.