You do realise that you don't have to use the exact same card for SLi don't you? Any 970 will work but I would stay away from EVGA cards as they are a bit odd.
I don't know which cards I use. I have two now. One is an evga the other is the msi. And sli will not work.
If you have an EVGA 970 then that is the problem, EVGA have knackered SLi on the 970's because they are idiots. Sell that card and just buy another 970 that is not an EVGA one.