I guess you have an R9 280(x) / HD7970 (becouse of the 3gb of vram). These card consumes a lot of power so you should have good airflow in your case. 90°C is a bit high except if you have ref. cooler. Solution: buy a new chassis with good airflow OR buy a water cooler for your VGA OR you can try undervolting it, maybe set MAX FPS/use V-Sync in games (you can do this from driver).
The card can (and will) pull about 300w, that's a lot of heat to dissipate. My friends ASUS 390 also exhibits the same behaviour i.e 90c+ if left at auto or 80's with a more aggressive fan profile.
The Sapphire cards had the best cooling for the 200 and 300 high end parts, the Accellero Xtreme also works wonders with them.
Have you checked the fans on the GPU to see if they are spinning?
My XFX 280X Idles at 32C and max gaming at 62C, but I have 13 fans in a Corsair 900D, so great airflow.
I also clean my case , filters and air coolers (Both CPU and GPU) about every month. This really helps.
If you blow out the dust on the GPU, touch the fan so it doesn't spin, to not over spin the fans
I also use "auto fan settings" and Set Frame rate control to 60fps.. I Do however run everything (games) at max settings.
Good luck, and try to increase airflow.