Random problems only while gaming (BSOD, CTD); multiple games affected

I have recently assembled my computer. During normal non-gaming use, I have yet to have any type of issue or problem. However I have had numerous stability issues while gaming and have yet to determine a cause, so I'm hoping to get some assistance.

While gaming, I have had occasional Blue Screens of Death and frequent crashes to desktop. Unfortunately, I haven't noticed any pattern on what typically causes these issues to happen, and so it has been difficult for me to diagnose it. I may play for an entire day without issue, but more frequently I would have several instances in a day. This seems to affect all games that I play & have tested (most of which are on Steam: Civ 5, Skyrim, Empire and Shogun 2 Total War). Oddly enough I haven't had an issue with Diablo III, which led me to believe for a time that it was a Steam issue; however, I've recently purchased Starcraft II and have had CTD's with it too.

Over many weeks of trying to figure this out myself, I had attempted to uninstall/reinstall the games affected, the graphics drivers (which I thought were the issue initially given that it was limited to gaming issues only), and drivers for all parts of the computer. At a certain point, I decided to reinstall Windows and the newest drivers (with no other software), but to no avail as the issue persisted, leading me to believe I've got a hardware gremlin.

I've also tried letting MemTest86+ have at it for a few hours (no errors) and replacing the graphics card for a few days with an older XFX HD 5850 left over when my brother upgraded his graphics card (still no luck, same thing).

I have attached two zip files from the SF Diagnostic Tool, run almost two weeks ago. I think both of these were after CTD's, so I'm not sure if it's going to have the information you're looking for, but hopefully it'll help.

I'll try to work on any suggestions as soon as I can, but if there is a short delay in response, this will either be because 1) the problem itself is intermittent, it may be a while to see if a suggested fix has the desired effect and 2) life will still get in the way sometimes, but you know how it is :). I appreciate any help I can get on this.

Thanks for your quick response. Followed your advice on MemTest86+. Let it run overnight and through this morning. 15 passes, no errors. Will continue with the advice on the Driver Verifier next.

Sorry for not posting sooner. Driver Verifier hasn't seemed to have triggered anything yet. And the system behavior isn't quite like it was before, in that I have yet to get any type of BSOD when I've tried anything since starting this thread. I have had a couple of cases of crash to desktops but that's about it [using mostly Civ 5 and Skyrim]. On Skyrim, in some areas where it looks like the scenery would be relatively graphics intensive, I've noticed some artifacts and a slight amount of screen flickering but nothing else yet to report. I'm also going to try some more Shogun 2 this weekend since that caused more frequent issues. Any suggestions on diagnosing the CTD's until I can somehow get a BSOD?