Basicly its probibly in need of a tune up....
new plugs, new rotor arm and dizy...
and some type of injector cleaner mainly the strong stuff like forte specialist injector cleaner, or slick 50 fuel system treatment!
this should bring the car up to performance.....
does the engine get revved high, do you do lots of short jurneys?
low revs and short jurneys tend to clog the motor up more..... this is why its good to open engines when their warm to allow the oil to circulate around the engine and to remove any water condence from the oil, this also helps to burn crap off the pistons, injectors and valves due to the high rpm and heat!
i like to take my vr6 for a 3rd gear high rpm blast down the local carrageway, i let the rps stay at aound 5000 rpm for a few mins!
you would be supprised how much better the car feels after! but obviously only give the engine a good blast if you know its been well looked after and the oil levels are always over minimum etc!