Hi
I had similar CTDs with my PMDG planes (737, 777) in P3D on long flights (+4h). After reading alot here and in the P3D-forums I installed the P3D-SDK for the P3D version I use and I stopped using all of the popup windows of the planes (no PFD, ND, CDU...). Since then the only CTDs I had was/is an OOM from time to time. I do not know if one of the two or the combination worked for me, but it worked.
Greetings
Enrico Reiser