I remember having a similar issue back a few years w\ AHII when I was using my old Intel C2D E8600 CPU on an EVGA 780i FTW mobo once I upgraded the vid card from an EVGA GTX 470 FTW vid card to an EVGA GTX 560Ti vid card. I started getting the very same type of screen freezes that are happening now.....my box never CTD but I would start getting the freezes after approx. 25-30 mins of gameplay. Pull the 560Ti out, reinstall the 470 FTW and all was well. Pull the 470 FTW out, reinstall the 560Ti and the freezes would return.
For a long while I was leaning towards the 560Ti card being bad but I never got any CTD's or BSOD's using it (which will really help to point to a bad vid card) so I held onto it.
When I built my X79 box that I was using until recently I fired it up w\ this same GTX 560Ti in it and I never had 1 issue w\ it doing any of this on the X79 box.....exact same card using the exact same drivers I used before but on a different platform...............
What this showed me was that it was not an issue w\ the vid card itself, but that this particular vid card needed a platform that could feed it data faster and more consistently so that it could perform properly than the platform that I used it on prior. At the time both platforms were using PCI-E 2.x spec lanes (initial X79 CPU was the I7 3820) which kinda paried this part out but the big difference was due to the Nvidia chipset\mobo layout of the 780i mobo (similar to the current AMD 9xx chipset\mobo layout) vs the Intel X79 chipset\mobo layout of the Rampage IV Gene ROG mobo (especially the CPU side of this design) as the X79 layout could feed the GTX 560Ti vid card MUCH, MUCH faster and FAR more consistent and the results clearly showed this even though I had the C2D E8600 OC'd to 4.0 GHz vs the I7 3820 running stock (stock turbo boost clocks were 3.8 GHz).
Now w\ my current box I have witnessed the same freezing but have seen it occur very rarely on my box.....on avg a 1-2 sec freeze every 2-3 hrs of gameplay usually associated w\ more numbers online and\or low alt flying (where the vid card will be taxed the most). I recently went in my box's UEFI and set the I7 5820K CPU to turbo boost to 4.0 GHz instead of the stock 3.5 GHz and this has shown to actually help my Fury X to run even better......now I might see 1 1-2 sec freeze every 2-3 hrs of gameplay. I have never experienced a CTD while playing the release vers of AHIII...only once trying to start the game. I sent in the only .dmp file that was in my AHIII temp folder and it was nowhere near the size of the files of others after zipping it to post it on the BBS so I would be curious as to what y'all saw from it, Skuzzy........
I have lately gotten kicked out due to lost Internet connections though as for some reason I'm having a hard time maintaining a UDP connect (switching to TCP connect soon after tower is up) even though I haven't touched none of the settings in my ADSL modem (Zoom X7N) since I originally set this sucker up some 3 yrs ago and had no issues maintaining a UDP connect until lately.......... My belief for this is due to my DSLAM as I have noted ping issues depending upon the amount of data traffic at certain time frames and this also could be the culprit for the freezes that I do see on my box.
The hard part to pin down is what is actually the issue that is causing this as the variables are very varied and any\all of them could be true.
I do hope that this can get sorted out for all of us. The thing though is that the "fix" may be varied across the myriad of platform setups the AHIII client is being run on.