A while ago I read about someone having their ecu re-set and noticed quite an improvement in not only performance but economy as well.
Do ecu's go 'out of tune'?
Perhaps trying to re-calibrate themselves to different petrol types has something to do with it? I don't know!!?
They (sorry I've forgot who it was) mentioned they had this done and a full diagnostic check at the same time for about £16!!???