Seems you did things right here...but I’m afraid it’s not coming from SH3 nor GWX...cause i can run GWX/NYGM/Ccom from morning to evening without a single CTD
It has to be something on your side, maybe a background program eating your RAM, or maybe a corrupted mod somewhere...dunno.
Have you tried to run SH3 vanilla game without anything else?
Have you tried SH3 patched with only GWX mod (no others) and the 4GB patch?
Have you unchecked the read only property of your SH3.exe?
Honestly really should work.