Yep, that seems about right with me as well. I've got the 2.4JTDm engine and get around 36-38mpg on long motorway runs. But for general driving around, the average works out to aroudn 27mpg. Nobody can get 41mpg out of this engine for any realistic form of "combined" driving. I was somewhere between gutted and enraged when I realised that the quoted mpg (the reason I bought the diesel over the petrol) is so utterly misleading. I have complained many times and just been told to live with it. My MPGs did improve a little when fitting a Bluespark tuning box, but this could be a false excitement since the computer doubtfully recognises the boxes modified injection pulses.
As for the gearbox... Well, there are lots of discussions on the forum about that. It seems you can be lucky and get a good gearbox or you can be unlucky and get a bad one. The trouble is, if you have a bad one, nobody seems able to guaratee they can fix it. The gearbox is absolutely the worst thing about the 159. Mine is dreadful going from 1st-2nd (stiff, notchy and really on the verge of grinding the teeth) and pretty bad also from 2nd-3rd. The garage have told me this is 'normal' and that a replacement offers no guarantee it will improve.