Lower hashrate with more then 1 card why?

[Valhalla]

Hello,

Currently I am mining with 2 GTX 780s. One gigabyte and the other reference EVGA. Both cards get the same 17.7MH/s alone, but when I mine with the two together, one hashes at 17.7 while the other does 13.6. Which card hashes at the lower speed alternates seemingly randomly. Does anybody have an idea how to fix it?
I'm running it off my gaming PC i5 4690k, MSI z97 gaming 7 and a 700 watt PSU, so it should be fine. Any help would be greatly appreciated.

I'm using windows 7 with 372.54 drivers (recommended online).

I intend to add around 2 more cards VIA risers, but would want them to run at max performance, not slow like one 780 is right now.

Thanks!

[2FA]

Temperatures of each while mining?

[Himommies]

I don't bitcoin mine but does it change hashes when you change PCIE ports

[Valhalla]

13 minutes ago, DeadEyePsycho said:

Temperatures of each while mining?

like 71 on windforce and 84 on gigabyte. Tried turning fans up to max, both were under 70 at that point, no changes.

[Valhalla]

13 minutes ago, Himommies said:

I don't bitcoin mine but does it change hashes when you change PCIE ports

I can't get the card to fit in my 3rd PCIE port. It's 16x, but don't know why it won't fit. Crappy mobo design I guess. It can't go all the way down.

[Ninetales]

4 hours ago, Valhalla said:

I can't get the card to fit in my 3rd PCIE port. It's 16x, but don't know why it won't fit. Crappy mobo design I guess. It can't go all the way down.

Don't worry, that's not correct information anyways. If your cards are getting various hashrates check temps, driver updates, change your pool/miner. I have 5 GPUs on my rig and have no issues and they all run at average or above hashrates.