I used to have a Stilo JTD which had some issues like you describe following a remap, never did get it fully sorted
Assuming your car is remapped and you are maxing out power from low revs..... sounds like you are getting a sudden cut out (like a limp home mode) then the problem may
be the MAP sensor.
That is what Peter (ex GSR.... remember them
) and I reckoned was the problem following a Red Dot remap. Initially it was thought to be the GSR induction that was fitted the same time as the remap but this proved not to be the case. Attention moved to the MAP sensor but unfortunately I am in Scotland and Red Dot & GSR were not so a satisfactory solution was not found as long range diagnosis just doesn't work.
What I couldn't find out at the time was exactly how the MAP sensor was causing an issue, but the suggestion was that it wasn't up to the job with the remap - too low a value. A 3 bar sensor was mentioned, but never found/fitted. Mine was a JTD 115 remapped to 150+
According to the Bosch specialists in Aberdeen the original sensor should have been fine depending on how the map was 'written'. Fuel pressure was checked - just in case - and was more than up to the job. Apparently.
It's maybe something to look at but, as yan.ko says, you really need the diagnostic information to come up with an answer.
In the end.... I bought an Alfa.