Things I can think of - first, try converting the mesh to quads in Blender (I believe there is a command to do that but I don't use Blender so can't be any more help there).

I have seen this kind of shading issue occasionally when I've been modelling in another app, and the solution there was to delete the vertex normal map. When exporting from Sketchup as OBJ, is there an option to preserve normals? If there is try exporting with it on and off, see if there is any difference. (I believe that Poser should ignore normals if they are in the obj and calculate them itself, but still worth a shot.) If not, try exporting from Blender in case there are more export options for OBJ.

When importing OBJ files to Poser there is an option to 'Make polygon normals consistent'; try importing with this on and off to see if it makes any difference. You could also try using FBX as the file format just in case that makes a difference (the current beta of Poser is up to date with FBX format).

A last possibility is to try adding one level of subdivision as this will create new geometry, but as the mesh has not been built for subD it probably won't work well ;)

----------------------------------------

Not approved by Scarfolk Council. For more information please reread. Or visit my local shop.