2.5 bmw roughness

I have just got a rr dhse 2000. It has a powerlink box fitted >The engine has a pronounced "roughness at 1400-1600 rpm. I am a bus mechanic so i am fairly familiar with diesels though not as fancy as this.I have checked the usual suspects , crank damper, angine mounts etc no joy, also the autobox to pedal position action seems odd, not much happens then all hell breaks loose,not too good for cruising.There are no warning lights on the dash lit. any Ideas ? could the powerlink box have something to do with this? thanks