Plug Wires

[Kracka]

*If* you installed the wires correctly I highly doubt they would make your car feel slower. What else did you change at the same time or around the same time? There is a possibility that the wires are faulty, but that can be checked simply by hooking up an ohm meter and measuring the resistance. The guys at Checker should be able to do that for you if you don't have a multi-function voltage meter.