Etherum and zcash need a different fine tuning on the cards . different Overclocking/undervolting.
my suggestion :
- reset all overclocking settings , uninstall display driver  , use DDU
 https://www.wagnardsoft.com/forums/viewtopic.php?f=5&t=823&sid=193bf6b90fd95d6daf88b38bafe75435
- Install display driver , dont overclock yet
- try mining zcash without any overclocking
- if its stable , start overclocking step by step

it might help

I have an Asus board which kept crashing in Nicehash during benchmark but once I changed in the bios the PCI-e configuration and put from Auto to Gen2 now it is working like it should. Try to change this at your board and give a try again to Nicehash. If it still doesn't work then go to option 2 below.

Option 2.
Back on topic why don't you try Zec Miner 0.2.0b, I used to mine Zcash before going to Nicehash with that software from EWBF and it never stopped, it kept running for days long without any problems. GPU-s used were GTX 1060 Palit Storm X 3GB.

You can try to run with an automatic software like Nicehash which can be downloaded here https://www.nicehash.com/?p=nhmintro

It mines automatically the best coin for you or you manually select which algorithm to mine. By the way I am impressed that GTX 970 is making more than my GTX 1060-s. Have you overclocked it and what brand are your graphic cards ?

Etherum and zcash need a different fine tuning on the cards . different Overclocking/undervolting.
my suggestion :
- reset all overclocking settings , uninstall display driver  , use DDU
 https://www.wagnardsoft.com/forums/viewtopic.php?f=5&t=823&sid=193bf6b90fd95d6daf88b38bafe75435
- Install display driver , dont overclock yet
- try mining zcash without any overclocking
- if its stable , start overclocking step by step

it might help