CHANGED FUEL FILTER, SPARK PLUGS & WIRES, REAR O2 SENSOR, AND BANK 2 CLEANED ( DUE TO A CODE OF LEAN ). PUT FUEL INJECTION CLEANER IN THE GAS TANK, BUT VEHICLE STARTED TO " PUTT " A FEW HOURS AFTER. MANY CODES HAVE COME UP; CATALYTIC CONVERTER, O2 SENSORS, MISFIRE IN CYLINDER #4. REPLACED SPARK PLUGS, BUT THERE WAS OIL/DIRT AROUND THE PLUG. ANY MORE NARROW IDEAS OF WHAT IT MAY BE? FUEL INJECTORS, EGR, MANIFOLD, CYLINDER, VACUUM LEAKS, CATALYTIC CONVERTER, O2 SENSORS???