GTX-970 is no longer detected after the 2015-003 update. To fix this issue, please check out this link: http://www.tonymacx86.com/graphics/159885-security-update-2015-003-breaks-nvidia-web-driver-again.html
It works for me.
I'm tying to remember what i did exactly since i did the upgrade a couple of days a go and I ran into so many problems.
I believe I always boot using the motherboard boot option to avoid that "mach_kernel" error. After the upgrade was successful I still have to boot from the usb one more time...