Thanks for posting everything in such detail. I have had issues getting my GTX-960 up and running without issues but after following your directions I was able to finally get everything working and it appears to be pretty solid too. This is my first hackintosh build so with everything being new your post really helped. Thanks for taking the time to share this with the rest of us. Tom
You need nvda_drv=1 in your boot arguments. Did you set any other options? Some plist configs will give you issues.
Which port are you using? DVI? DP? Where is your org.chameleon.boot.plist located? You say sometimes it works sometimes it does not. Can you pin down the change between when it works and when it does not?
If this issue persists you could try out TylerWorth's Clover install. My system is much much more stable with Clover. Don't always do exactly what TylerWorth does, though. Look at the main Clover guide as well and try to understand what settings you actually need.