I am a bit confused by your post.

You said you downloaded GWX Gold...from your post I assume you install it and it work correctly. You next said you installed WAC 5.0..did you uninstall GWX and do a clean install of SH3 then attempt to install WAC which gave you CTD's?
Kelly621
I use the original disk version of SH3...I am not a steam expert and handling SH3 is a bit different with steam. Fortunately, there are a number of folks here with the Steam version that know their stuff and I am sure will help you sort this all out.