Along w/Steve on the plugs... change the coil connectors under each coil ..
Not only are they known to cause igniton faults,but the ECU on those waste spark systems shuts down the injector when an ignition skip is detected , compounding the symptom...
They are cheap and that is one of the few recommended 'just change them' parts..
Remember , on this type of ignition system, the spark has to travel through these connectors to reach EACH of the 6 combustion chambers b/c each coil feeds 2 plugs [ they are wired in Series]
So, the skip can be more pronounced under load...
[ usually resulting in slight miss at idle , also]
The fault is not usually the resistor in the boot, but rather the spring that tension connects to the plug tip.. My opion is that it is a weak connection from design and fatiques early due to trapped heat. Whereas the other 3 have a solid Snap connector that seems to hold up well and air circulation is better than the the coil on top three..