I had a similar problem with my 2.4 Brera a while back, and had it looked at by the garage (under warranty, although that turned into an argument). The turbo boost keep rising up on a journey (my commute is around 20 minutes up the A3, effectively a motorway, with a bit of urban either end), producing awful MPG. It seemed to be a regen, but it started happening virtually every journey.
It seems to have come back, although not has bad. Basically the performance has become "lumpy", with hesitation in acceleration, especially at low gears. The turbo also rises a little when it shouldn't. The computer MPG is also variable, but frankly that seems random.
My journeys are often fairly dull, with little opportunity to give it some stick and wake the engine up, so I have tried giving it a little more enthusiasm when accelerating recently (where possible).
Any ideas - likely to be the DPF? Or just maybe some dodgy fuel?
The worst element is the performance, it just isn't as much fun! It is also dragging towards a DPF/EGR removal, especially now the warranty it came with has run out...