I was having a similar problem as you were. I have a similar rig and have similar add-ons. Two hours into transatlantic --> CTD --> again, again, and again. I fly the PMDG T7 and 737ngx. Then one flight I used the 737ngx --> I didn't load any flightplan into AS4D or P3D --> flew for 6 hours straight and no CTD. I thought I might be on to something --> so in the T7 I turned off upload flight plan to AS4D/P3D and voila --> 10 hour flight without CTD. So for me I was able to alleviate the CTD by doing all flight-planning on the FMC and not allowing the flight plan to be uploaded into AS4D/P3d. Only annoying thing is the AS4D keeps asking for flight plan to be loaded via the green message bar.
Give it a try.. might work for you too.
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