I doubt that the plugs are causing you any problems yet, but they will not last as long as double plats.
I too would suspect your wires. There have been several posts about problems with the FMS wires. I have a set and they are working fine for me.
Before trying another set of wires, try cleaning the injectors and also if you can find a know good coil pack try swaping it. These are probably more likely to be a problem than your wires.
