UPDATE: I went ahead and created a new folder and reinstalled everything, then the update. I was playing just fine, one whole map and then boom...black screen again...with a bit of digging, a friend asked about the downloadable content. Ah, ha...I had purchased not only the game but the extra content, but somehow, the update deleted it??? Not sure, but anyway, I copied my file from steam and voila! The game is running smoothly!
I'm still sure it was a user error issue, just don't know exactly what I did to lose the DLC. But that seemed to fix it all. Hope that this helps anyone else with this issue.