While the face normals (the one from a center of each triangle ) looks perfectly up those normal are derivative as a median of vertex normals in triangles corners. The bottom left corner for example , clearly not 90 degree up . it's what creates shading gradients. Face weighting, or direct normals editing could fix it .…
Dumb question, but in the Preferences do you have FBX set to export smoothing? It's, for reasons beyond the comprehension of mortal man, off by default.
If it helps, the problem occurs on the bottom section of the model if it helps even more the render that I have provided is default scanline render with no lights.
Now incorporated as the default in max, but still available for other versions - have you tried this? http://www.guruware.at/main/index.html Maybe it will help? :)