To work with cad files, these have to be cleaned:
Cad files by nature, have always duplicated faces, and custom normals (cad geometry uses normal data for internal purposes, particularly ACIS data, this is reflected on any exported file). (Specially autodesk generated files), first is to clean them, since nvidia cards seems to have problems with any double face geometry anyways.
In 2.7 use this script:
C = bpy.context
scene = C.scene
C.tool_settings.mesh_select_mode = (True, False, False)
for ob in C.selected_objects:
if ob.type == 'MESH':
scene.objects.active = ob #set active object
bpy.ops.object.mode_set(mode='EDIT') #switch to edit mode
bpy.ops.mesh.remove_doubles() #remove doubles
bpy.ops.mesh.tris_convert_to_quads() #tris to quads
bpy.ops.mesh.customdata_custom_splitnormals_clear() #remove custom normals
bpy.ops.object.mode_set(mode='OBJECT') #switch to object mode
You will need Blender 2.79 to make it work (for now, i don’t care about 2.8, so i don’t experiment with it), import your cad file in 2.79, paste the script in the text editor, select all the geometry (in the 3d view, press “A”) and press the run script button. Depending on how big is your scene, you will need to wait some time (half an hour to one hour).
Save your file and open in 2.8x, should be workable. (at least, in 2.79 sure cleaned geometry is).