Changed out sparkplugs,wires,coil pack and code PO303 came up again.Car hesitate

Have it diagnosed by a reputable repair shop. Misfires can get costly with guessing game. Possible ignition problem, Scoping it should further shed some light on ignition faults. Check fuel system also, a failed injector cyl. 3 can be the cause. Or it can be mechanical, cylinder compression test and leakage test can be performed to check mechanical integrity.