OK, I figured it out. The GTX-960 has three DisplayPort ports and only the one on the end, closest to the HDMI port seems to work at 4k with these Active DisplayPort-to-HDMI dongles. I bought a different dongle in case the CAC-1070 was malfunctioning and it also ONLY works at 4k on this first DisplayPort port. This information IS NOWHERE that I could find on the internet after days of searching. What a waste of time!