i wouldn't say knackered but not the best.
try a good strong injector cleaner for a tank of fuel and check again.
try the plug disconnect clean terminals and reconnect(elec contact cleaner)
you could try logging a few extra things to check out , a short drive with revs desired boost (mbar)and actual boost and maf(mg/I)
might lead to something for poor mpg like a boost leak etc
also you could log revs, desired boost, actual boost vnt%
if those readings were 2000 rpm driving what sort of values does it do no load(parked neutral)just idling and then reving to 2000rpm?
also a log of desired fuel pressure actual fuel pressure and pressure control % might give some clue , a blocked injector or overfuelling injector might give abnormal % amounts( im used to 30% to 40% range)
then I suppose you've got service items (for mpg)
air/fuel filter/oil filter n change
brake calipers sticking