How can I fix my BMW 318 Ci 2000?

It feels choked and only drives smoothly at low revs, if you put your foot down a bit it judders and really hardly moves. It has had replaced or checked already: Catalytic Convertor, Lamba Sensor, Back Box, Airflow Meter, Fuel Pump, Fuel Pressure. It runs fine and ticks over well, but has to build up speed very slowly. The mileage is 130k, but from the SH the 1 previous owner and the appearance, it looks very well looked after.

What do I check now, or has this car had its day? Ive had it only two weeks, and I know Im stupid but it was a private cash sale from an unknown person. It has FBMWSH and has been mileage and HPI checked. It drove very well to start with.