everything looks good to me.
are you using the disp exporter to export your disp maps?

i dont usee that thing and i get pretty good results with 16bit tiffs.
simply exporting the old way.
i would also use a normal map instead of a bump map.

not much more i can help with. all seems ok from those pics.
the problem must be with Z and not maya.
chances are its the maps themselves.