I don't know of any program that can test a graphics card to see if it is bad. However, it would be helpful to have some clarification about your Flight Sim issues. Have you run the game before which the graphics looking good on high? If so, then it sounds like your card might be switching to software only mode which can cause the grqaphics to look pretty terrible. In my experience the graphics for Microsoft Flight Sim aren't particularly good, accurate perhaps but not great.
Ok, it sounds like you've just got this card, have you added to a relatively old system, perhaps a system that was previously fitted with a low end card? Your problems could be caused by either a power supply that is faulty or unable to supply the amount of power required by the card, overheating - how well is your system cooled? Have you tried running it with the side panel off? Do you have a large desktop fan? You can try pointing this at the internal components with the side off. If the system runs ok in this configuration it is likely that you need better cooling, or perhaps a better case or maybe you need to have fewer cards inside your system. Are you overclocking anything - if so, try resetting everything back to the defaults and see if you have any joy.
These sorts of problems are nearly always caused by either a lack of power or by too much heat which is either a result of insufficient colling or by overclocking a system beyond its limits.