I just installed a 2nd K5000 gpu into my Mac Pro Tower. When I opened a project up in FCPX, playback was extremely jumpy and when I tried making simple edits the program would respond wacky. For example, value changes that I would make in the effects window would appear on clips that weren't selected. I suspected that the new card was probably at fault, so I turned off the Mac and removed the original k5000 gpu. After rebooting with just the new k5000 installed, FCPX worked perfectly fine. I then tried turning on the Mac pro in several different configurations, i.e. old card in slot 1 & new card in slot 2. Then new card in slot 1, and old card in slot 2. New card in slot 1 by itself, new card in slot 2 by itself etc... Pretty much, regardless of the slot, when the cards were installed seperately, fcpx ran perfectly. Installed together caused fcpx to go crazy. I was running Yosemite so I upgraded to El Capitan to see if that would fix the issue. It didnt. Ive made sure Im running the latest drivers for Nvidia and nothing. The issue isn't that two GPUs are installed because the 2nd k5000 just replaced an OEM Radeon Apple 5870 that has been running in conjuction with the 1st k5000 for the last year and a half without an issue. I can't figure out what's wrong. Anyone got an idea as to what the issue might be? My machine's specs are: 2 x 3.46 GHz 6 core CPU 32 GB 1333 MHz DDR3 1 TB Crucial SSD Boot Disk.