did u import an R33? congrats.
by lack in performance what are you comparing it to? a couple people here have CA18 and RB20E R33 GTS... Check if you have one of them.
Pretty much what Greg said, and I'd do the fuel filter, radiator flush, spark plugs, gearbox oil, differential oil, brake bleed, new brake pads probably.
These are relatively old cars, so they need a lil more attention - and the peace of mind knowing that every fluid/filter is changed is good.
A dyno run would show if the engine is running ok too.
Eug