Vauxhall Vectra CDTi SRi 2004 Loss of acceleration and lumpy running ?

My Vectra has had a full service, new Cam belt, and is still running lumpy at idle and at low revs ( in 1st & 2nd).

Has a loss/restriction of acceleration up through the gears, it runs slow and as if choked while trying to accelerate only to suddenly clear and take off like a bullet out of a gun. Runs fine on the highway.

Recently had a particulate filter re-gen after going into limp mode and then the alternator went... it still has this problem. Some days it is better other days it is appalling. Try to pull away at a roundabout and just drift at 2mph into the traffic with no acceleration !! Seem to have some white smoke as well at start up. I need to know what is wrong and what I am looking at to fix it.