Does it feel like a stutter at 2500-3000rpm? If so its totally normal. They all have these, its a flat spot in the map. Some say a remap will make it better but mine has been remapped and although better the stutter is there, its made worse by the lightened fly wheel and ported TB as it excentuates the effect.
You will also get what feels like driving into a strong wind when cruising at them revs, this is caused by the EGR system, again totally normal.