gu patrol gearbox continued & tuning 4.2td

hi all
i am still waiting for spring to turn up from nissan,they tell me monday (hopefully).
the few times i have driven car i wasnt real happy with its performance
compared to my previous car which was a 80 ser cruiser with an aftermarket
turbo. a few people have suggested to me to have it tuned by (not allowed to mention name)
the tune consists of o/haul injectors,adjust tappets,adjust timing,fuel aneroid mod,turbo adjust & on road adjustments.
they claim this makes a big difference as the nissan motor isnt set up real good from factory.
i have since read other article about other diesel shops who also have tune packages for the patrol & am a little bit sceptical about claimed performance increases .(30-40%).
appreciate any advise on this.
thanks spudit
p.s car had new fuel filter in november.