Hey Jeffo31350,
Do you have any updates on this issue?
I have the exact same issue on my 2012 12-core Mac Pro with ATI Radeon HD 5870. I have the stock 12 GB memory, I'm running four 1TB HDs in software RAID 10 (1 + 0), with four 27" Apple LED displays. I am running Mac OS X: 10.6.8
One time in ten, or so, I'll put the Mac to sleep, the fans will spin up, the light will flash like it's sleeping, but the fans will never spin down, and it's impossible to wake the Mac. I am forced to reboot at this point.
In my Power Management logs (/usr/bin/pmset -g log) I see the following sort of errors (the only thing that changes is the date):
* Domain: sleep
- Message: Sleep: Drivers Failure panic - AC - IOU0 HDEF SATA
- Time: 9/5/12 11:05:48 PM MDT
- Signature: Drivers Failure panic
- UUID: 2391C1EB-1D5B-4530-8FA9-42D2430C3D16
- Result: Failure
I'm curious if this is the ATI card as I have historically had bad experiences with ATI and Macs (as well as the above comments from Carolus730), and video cards do have a higher than normal instance of causing kernal panic issues...