chris, which window are you exporting from?
the two options i would try are these:
1) capture view as 3d document (right-click and select option from context menu) and export to dwg from 3d document window or,
2) set 3d view to use 'internal engine' (instead of opengl), enclose the required view with a 2d marquee and cntrl-C (selecting the measured drawing option). Paste this to a 2d window (e.g. plan or worksheet) and then save as .dwg.
the first option i think is better as you can more quickly update the view and re-export if required.