I think i have a problem. Can anyone help?

[Alastair]

Hi people. As the title says i think i might have a problem, so im looking some help to solve it. I have an 01 b5.5 130tdi saloon that is currently mapped to around 180bhp. It has been mapped for about 5 or 6 months now with no problems. Recently the car has had a full service including timing belt kit, clutch kit, pd oil, oil filter, k+n panel filter and fuel filter.

Now i was out and about last night and going through the gears as normal, but when i put it into 6th at about 50mph starteded to accellerate, when the car was under load it started to hesitate slightly just as it was under load. It cleared itself once it went up the rev's a bit but i did it a couple of times and it did it everytime.

Just wondering if anyone has had any similar problems and if so could you guide me in the right direction

Thanks.