While idling; I've pulled cylinders 5 and then 6 plug wires individually and there's no difference in idle speed. Both cylinders have 150psi of compression. Plugs have been changed twice. Plug wires, coil and tfi have been changed as well. I tested spark on all cylinders with the tool that goes between the plug and plug wire. Spark is orange on all cylinders. I haven't done a leak down test. Car ran great right up to this point. It's weird that two cylinders side by side are affected and they also fall in line in the firing order. Valvetrain?