Ford Repair: can you help me, ford mustang, cyl head

Question
hello I have a 2002 ford mustang with a 3.8 liter V6, my check engine light came on and gave the codes P0316 and P0303, the car is stumbling at around 30 to 45 mph at 1300rpm, i looked up the codes and it said the car was misfiring on piston 3 i replaced the plugs and wires and had no change, i replaced the filter and that made some change but it still stumbles, can you help me with this problem?

Answer
Hello Andy, I have seen a few vehicles with those codes that relate to compression leakage from around exhaust valves. The way to correct it was to replace the affected cyl. head. A ford dealer can perform a cyl. leakdown test to verify cyl. leakage. There was a message on 2003 model vehicle but I can't find the # for it. Hope this helps Thanks Tony