So even in Nicehash excavator Equihash miner the same problem ? If this is the problem I don't know what to say, the first time I hear such problem and is the strangest I have ever encountered so far.
Why you want to mine Equihash in the first place, I know the GTX 1070 is the best bang for the buck for Zcash but even in Ethereum they should do 32 Mhash with a bit of overclocking. It is the same profitability, I have a Gigabyte GTX 1070 and it does 450 sol/s with EBWF cuda miner.
I also have GTX1060 3GB rigs. They have the same problem sometimes. But they works usually.