Hi sncooper,
Here's a long shot: Try resetting the SMC. I have a much-older MacBook Pro, which, for reasons known only to it, sometimes decides that it's not going to bother using its fans to cool the system. The result is just like you describe: Random graphics hangs, with a bunch of NVDA log messages about "PBDMA error" and so forth, at which point I realize that the rear of the system is screaming hot and the fans are not running anymore (or are running so inaudibly slowly as to be making an insignificant contribution to cooling the system). If I reset the SMC, I can hear that it starts using the fans again, and the system works relatively normally... for a while. After some small number of days, it goes into the same state again and hangs while attempting to cook itself, and I have to reset the SMC again...
Hope this helps!
--
Darius
