the GPU is bad. I just have a feeling. 

there are multiple routines and calls that a GPU can make, and they take different paths in the core to render things. for example, drawing, sprite rendering, 2D rendering, 3D rendering, simple framebuffering are all different. 

if you have stock installation media, and its not working, replace the logic board. 

In a rare case, if the GPU shares its graphics RAM from the system RAM, try swapping the system RAM.