One card is slow, one is not?

I tried searching the forums and couldn't find what I was looking for, I am sorry if this is a duplicate. I recently bought a new motherboard that has several PCIE slots and wanted to run two 5830s on it. Up until now both of the 5830s were mining on two other PCs and both ran fine, and both were running linuxcoin. I put both of these on the new board and created a new linuxcoin stick and started mining. This does work however there are two problems.

1. The card in the PCIE x8 lane can not be overclocked, if I use atitweak or amdoverdrivectrl the card will fall to 0 Mhash. The value I try to set does not matter, even if all I do is underclock the memory. This card works normally on another board. I can overclock the first card with no problems at all.

2. The same card with the first problem runs only at about 145 Mhash without overclocking. It also eventually stops mining showing connection problems to the pool even though the first card will continue mining.

These cards are not connected via a crossfire bridge. I am using DiabloMiner and I have started one session for each card separately, and together with no difference. When I start mining after a reboot, both cards run ~245 Mhash, the first card will remain there, the second will slowly fall and stabilize at ~145. Heat is not an issue, the first card is hotter than the one that is slow in any case, the slow card is at 63 C, the hotter one at 69.

Any ideas? I have tried the 2.1 SDK, no change. I am using the latest linuxcoin. Both cards are Sapphires, same style and the motherboard is a Gigabyte 990XA-UD3. Thank you