First of all, do not use a vacuum to clean any computer parts - static builds up on and around the nozzle and could make for a sad ending. Best use a can of compressed air on the card to blow the dust to smithereens.
Does it idle at 53C with the fan at 100%? I have two 8800GTS 640MB cards in SLI and they both idle just under 60C at 60% fan speed (but doesn't really go past 76C on full load). GPUs are different to CPUs as they can tolerate higher temps (even so, 90C+ is too hot).
The issue could be one of many things - dust, faulty card, faulty temp. sensor, bad air circulation in the case, a mis-fitted heatsink on the card, or indeed a dodgy bit of driver code (though this probably isn't as likely, bar the recent issue the new nvidia card had where they kinda exploded). To be honest though, it is probably a bit of dust in the card which can be given the boot with the compressed air.
If you choose the compressed air route then the usual considerations apply - de-static yourself with an anti-static wristband or keep yourself grounded some other way (touching the exposed metal of a radiator maybe), put the card on a clean, flat surface (anti-static bag on a table for example), try not to touch the components on the card if possible, don't let the fan spin when you're blowing air into it as there's the (slim) chance that it may send a tiny amount of voltage though the card.
Bet you wished you'd stuck to consoles now, eh?

well i pulled the card from the board an did not use a vaccum (thanks for the tip close one) i dident have a can of compressed air so i went old school on the bich. Used good ol lung power (pot head lungs so lotta push).
Max the cards capacity out to 100 on the heaven unigine dx11 benchmark. let it run the whole thing an my cards now cool at it was before only reaching about 76celcius during gameplay and idling at 40c with 35% fan speed.
I FEEL LIKE AN IDIOT. had no idea dust could cause so much harm it mus hav killed my airflow!!!! Explains why so many of my old 360's died...dust=Overheat