Yes, we can rule out everything outside Maya. Just checking again, did you use photoshop to adjust heightmap in any way?
The thing you need to check, is the module you used to import texture. Wherever you set the detailed settings informing maya about the imported file. I personally haven't used maya in over 8 years, can't give you the specifics. I use blender, and it handles dynamic range of the image much better by default.