Slow start and rough idle wouldn't be caused by a cat. If the cat was completely clogged, your car wouldn't run at all. Are you getting a cel? If so, get it read at Autozone and tell us what it is.
It's more than likely a bad plug/wire. You need to go back through each plug and wire to make sure that they are gapped correctly, and that you didn't get the wires crossed. If all else fails take the new ones off and put the old ones on (You saved the old ones for a bit...right?) and then start swapping them out one by one until you find the bad plug/wire.
You can tell a bad cat by the very potent rotten egg smell that t gives off...that and the cel.