1999 Nissan Almera magnecor leads

Hi, i recently purchased a custom set of magnecor leads 8 mm. After removing my old set of leads and installing these performance leads the cars acceleration was much slower than before, i dont know why. Im also running nrk iridium ir plugs which also enhance performance. As well as a lack of power under acceleration it feels like a slight misfire.

If anybody has any ideas as to why i have lost that much power when they are designed to increase it?

Thanks shaun