Pull the plugs, gap them real tight (.02"), and try it out. 5500k is near peak BMEP for the engine and right where a weak ignition system might stop firing. If it improves you can concentrate on plugs/wires/coils, if it doesn't change then you've at least reduced the possibility of it being ignition related.
Narrowing the gap of the plugs to .02 will in itself not allow the coils to generate enough energy to spark anything in any resemblance of reliable fashion and is no way to diagnose a weak ignition secondary circuit. There are only two ways to diagnose a weak spark issue, a physical inspection of the related parts for carbon tracking or a bench test.
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