The car has done about 120k.

2 years ago the diesel injection pump was changed, since when the car has only done around another 4000 miles as we have been away.

Now the car is driving very erratically - sometimes very little power, and not pulling smoothly through any gear except first. The idling speed was all over the place and it frequently stalled on starting up and driving away in first. I took it in to the BMW garage who sorted it and now the idle is fine. But after about 120 miles back came the problems with the power.

I often have to change down to second (or sometimes even first) to get up hills which are not very steep, and always have to keep the revs up otherwise it loses power.

In addition, the yellow ATC light on the dash lights up as soon as I move into second gear, the consumption on the computer shows a delicious 99.9 miles per gallon, and the consumption indicator on the dash doesn't move unless I really rev up hard.

The garage tell me...the diesel injection pump needs replacing.

Can anyone help with what is going on here?