acclaturation labouring?

Hin there please could you advise, my vauhall vectra 1.9cdti has just in the last week gone on a labouring speed, got all the right revs but the zip is no longer there, untill it reaches high speeds.

I HAVE WORKED BACKWARDS in changing parts put now becomming expensive to put right.

It had a diagonose last week and it said the problem was to do with the fuel booster sensor, but cleared the fault and never appear again.

Please could you advise further