Why is my engine sluggish when hot for a while?

2003 Ford Focus.
When I drive for more than a half hour on a hot day, the engine will be sluggish and misfire while under load. I have checked several components and I suspect that the problem is either the fuel injectors or the spark plug wires.

Start with the inexpensive stuff, air filter, wires and plugs. Fuel filter if is not inside the tank. Check alternator voltage and current output and fuel pressure.

No improvement, see a mechanic with a scan tool and check live sensor data when the car is being driven with a hot engine. O2 sensors that are sluggish could be a cause. A clogged cat converter can also be a factor.

Hi the misfire is the coil pack breaking down electrically. So you need a new one.

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