I don't know what the issue is, I'm hoping it's something simple and not a hardware issue.
My original card is about 9 months old. Has worked great all this time. I just got a second card to run in crossfire, but there are a couple of issues:
1. The new card is running at 1100/1250 w/o any over clocking. Ok I guess, just don't know if that's an issue or not.
2. When I enable crossfire, the second card ramps up to 99% GPU usage, and card 1 does nothing until I lean on the system. So the bottom card runs stupid hot, like 13-15C hotter than the top at idel, and cracks 70C in 1080 Furmark benchmarks, while the top card hits about 55.
I have tried 13.10 Beta, 13.11 Beta, and 13.9 drivers, all have the same effect. Both cards seem to be running the same BIOS version, but second card seems to be running double the shaders... Both cards are HD7870-DC2-2GD5-V2 cards.
Rest of my system:
16GB GSkill RipJaws 14900 @ 1866MHz
HD7870 CF (problem)
Ultra LSP 750 (816W single rail)
Kingston HyperX 120GB SSD, WD 1TB, Seagate 160GB