PCI Express x16 slot problem that makes absolutely no sense HELP!

[mcfly85]

I have a gigabyte GA-Z68A-D3H-B3 MB with UEFI installed and a Gigabyte 550ti video card. For the first year with this board I was only able to run the video card in the x8 slot because every time I put it in the x16 the computer would crash when using accelerated graphics. This happend in windows, osx, and linux so it was not a driver problem. Frame rates were fine in the x8 slot so I left it alone. Gigabyte support could not give me a straight answer. I then upgraded to the UEFI bios and thought I would give it a try. IT WORKED! or so I thought.

When plugged in this slot Mountain Lion will not return from sleep. It works flawlessly in the x8 slot but will not wake in the x16. Works in windows without a hitch now.

Bios settings have been set to PEG first and I have done every scenario with the integrated graphics from disabling it to auto to whatever.

I also had to disable vt-d in order to get mountain lion to boot.

PLEASE HELP THIS MAKES NO SENSE

Core i5 2400
GA-Z68A-D3H-B3
GIGABYTE 550TI VIDEO
GENERIC FIREWIRE
NZXT PHANTOM 410

 

[mcfly85]

After a year... and one more try the card works perfectly.... no clue what happend. Since it is a 550 ti I have freeze issues that have not been resolved by any post in the 550ti freeze thread. Thus I have reverted to 10.7.4 for stability reasons until my next card purchase.