Clogged cat will cause misfires. Best cat test is back pressure measurement at upstream o2 sensor bung. Other indications are quiet weak flow from tailpipe, exhaust fumes blowing out of manifold seals in engine bay, weak acceleration in lower gears especially on upgrades, engine temp rise after laboring up a long upgrade. Mine did not glow red hot as others described.
If you have new plugs, but not new wires, change the wires, eliminate that variable from the equation before the expense of the cat decision has to be made. In my experiences with bad wires, you will for sure have problems with high speed misfires, and also under high load when accelerating at lower speeds, you will feel those and may not actually see OBD II misfire codes thrown. It may idle relatively smoothly, and even when revving in neutral, but go rough as soon as there is load put on the engine.
When you did your tune up, did you make the common mistake of putting the dielectric grease on the tips of the plugs and onto the contact surfaces of the connector inside the wire boots? The stuff is an insulator, the last thing you want on an electrical connection. Its just supposed to be lightly swiped on the rubber inner diameter of the boots with a Q tip to seal out moisture.
