Its downclocking into 2d clocks which means your pushing it too hard.  I find these cards OC to 1000 Mhz Core Clock very easily almost every time with no problems, thats where i usually have mine but iv tested mine up to 1022 Mhz Core Clock stable with no problems in any benchmark, anything more and it downclocks.
 
Try 1000 Mhz and see what happens and post back or up your voltage a bit, my voltage is at 1.112 and yours is at only 1.087 so that could also be it.  Keep an eye on the temps though when doing this and test it to see if its stable.

Sounds like your card is protecting its self from damage and clocking down on you,
but i heard it does that around 97 degrees Celsius so i dunno..
 
I have that same card and overclocked it a bit so i might be able to help.
First off lets not forget its ALREADY overclocked from the factory..
google the 550 reference clocks and see what i mean ;)
 
Also when i overclock this card with evga software or any others,
i get 0 artifacts and i simply get a driver crash (when gpu pushed too far)
and im using 301.42-desktop-win7-winvista-64bit-english-whql
i never did try the previous driver i just bought my card.
 
So with stress testing to make sure its stable the most
i can overclock this thing to is 971/2188 (at stock voltage)
if i put the core to 1,000 my OS crash's and lockups instantly and i have to reboot !
So i wouldn't jump up straight to a 1,000 if i were you
start at 10mhx increments and test for a bit then move up some more.
The clocks i mentioned (max) are within about 10/15mhz of causing errors,
so i wouldn't expect anyone to get more than that at stock voltage.
 
I can't say anything about higher voltage speeds though
i havn't tried that yet and i'm not too interested
it makes me a bit nervous over volting, even though i do it 24/7 on all other pc parts.
 
I'd love to be able to get it running at 1055/1260MHz
http://hwbot.org/hardware...rd/geforce_gtx_550_ti/
but i don't know what this guy has done etc
 
Lastly i did experiments with covering the outtake exhaust inside the case
and it made the temps way worse.
Although putting electrical tape to seal the fan so only air can escape
through the two exits seemed to help it blow air better :)
edit:
i also got a bit of improvement on load temps when i re applied the TIM paste
i used Arctic Cooling MX4
edit:
oh and i was suprised at how well the TIM paste was applied from the factory
they seemed to use something that looked and felt like Artic Silver or AC MX
and the application of it seemed pretty good, maybe a tad on the too much side
but i would tell people don't worry about the TIM on this gpu and only replace it if you
really want to because its perfectly fine from the factory :)

ya but explain to me how you stress tested 1,000mhz
any overclocker knows medium usage prob won't
show any problems until you go really hard.
and factor in the rising ambient temps (summer is coming)
i REALLY would not advise anyone running 1,000 on an 550 ti (with stock voltage)
I couldn't get no where even close to that with out windows locking up or oc programs crashing instantly.
so i don't think i just got a bad card
 
I'm not the only one either that gets these same results..
if you don't believe me go and google it ;)
 
I'm concerned some people may be misinformed or worse fry their cards
 
edit:
i better mention that i am using the FPB edition too

Sorry to bring this thread back up but i recently got the Card about 2-3 Months ago and today i been trying to overclock it i was wondering with a stock case on with 1 CPU Fan and Air holes on the side running Fan at 95% Clock at 985 And been running OC Scanner for 10 Mins heat at 75. you think i should invest in a new Case and so fan's? before i overclock this Beast! check my youtube @Foopszgaming also!

well im moved my computer now so its by A/C now i get about 67 Celsius as max when at 1000Hz
 

Fans at 95 i can run it lower though i i wanted to i plan on getting getting a New Case and Processor you no any cheap Processor i was thinking about going with AMD??? FX-8 Cheap but good for gaming i have a i3 Quad Core right now.
 
 
P.S How do i increase Shader Clock install a older version of Precision

Intel Core i3 CPU 530 @2.93Ghz 
 
Look it up pretty sure it's a Quad Core.
 
 
P.S i7 But a Big Hole in your Pocket! i would go with AMD can get a FX-8 Series for 160 if you can find that price on a i7 let me no!

Your i3 is a dual core. It has hyperthreading so it looks like a quad core to the OS.
 
Looking it over, your mobo is an older socket, so you're gonna have a problem finding an i5/i7 for it.
 
If you're looking to save a little money while upgrading, the new AMD piledriver core based CPU's might be good for ya.

If you know of any Cheap Motherboard's let me no and if i get a new Processor that would increase my FPS Right?
 
 
is the pile driver even out yet i need this stuff by july its my birthday in july!

Run Furmark for an hour
or OCscanner with the gpu safety feature turned OFF
and then tell me you don't get problems at 1,000
 
also lets not get confused here lol
there is more than one 550 Ti model
and the best i can speculate is there are similar
but not identical.
I have the FPB edition i don't know about the other guys here.
 
All i know is i can't get close to that in any program at all
(WITH stock voltage)
My case cooling is a work of art too
i have a system custom made and refined from years of experiments.. Basicly I've been trying for years to find the best way to deal with air flow etc using a variety of techniques and materials including 4 diff sized fans from super small to really huge. the result is my case is COLD :)
I'm so wonky i even put a digital therm diode on my ram lol
Was a waste though they don't even get warm on stress test apps (ram these days can take a beating)
 
You guys
I'd love to know what model number's you have
if you can hit 1,000 on the core with out problems (w/ stock voltage)
I'm not gonna call anyone a lyer I'm just curious why mine won't go that far. But I'm only considering a good OC is one that is stable on extreme benchmarks (which may not be neccesary)
 
edit:
I just looked at some earlier replies
and i see some people admitting to increasing the voltage ;)
That would be a pretty key point to make when your telling people
this card goes to a 1,000 core easily and safely with no problem lol
Leaving that tidbit of info out = your computer is gonna crash ahahha

well i didnt increse voltage and it ran fine i have use MSI Stress Test and EVGA Stress Test For about a Half hour on both of them i do agree i have problems somtimes running games one time my Mhz was at 70 for playing a might Downclock a little not worth overclocking to 1000Mhz i will over clock again if i do downclcock when i get my new CPU also check my Video on the 550 Ti at www.youtube.com/foopszgaming

i have my 550 Ti FPB up to 1.125 volts, with a 100mhz GPU clock, and 2200 Memory clock, i can play Battlefield Bad Company 2 on high settings with Anti Aliasing @ 32x CSAA, Anisotropic Filter @ 16x, Vsync is on, pulling 55 to 60 fps, with mid 60's C temps. Yet to give Battlefield 3 a full hard run at ultra settings but for the first mission the oc held out strong with no artifacts or problems.

Way to revive a dead thread. Also overclocks for one person might not work for another