jspringator, you mention the shudder is at 1500 rpm and below, so assume it smooths out at higher RPM? If so that wouldn't indicate an ignition problem....as supported by lack of codes...if one or more plugs wasn't firing the miss would be more noticeable at higher RPM.
Sounds like you are inclined to assume spark issues given your COP problems...but I would be more inclined to look at fuel/air for a roughness at low rpms.
Have you ever taken out the MAF and cleaned it? Air filter? Fuel filter? Fuel injectors? I did a MAF and throttle body cleaning and also pulled the injectors and sent them out to be cleaned, made a huge difference in idle smoothness.
