MacPro (Late 2013) Freezing

Hi!

I've got a late 2013 MacPro computer which I purchased a month ago. Since then, I've encountered random freezes which basically affects my work. I have clients sitting in during a session today and my computer froze up, it goes without saying that it was quite embarrassing having to apologise and restart the entire computer while in the middle of a session.

Here's my computer specs:

Model Name: Mac Pro

Model Identifier: MacPro6,1

Processor Name: Quad-Core Intel Xeon E5

Processor Speed: 3.7 GHz

Number of Processors: 1

Total Number of Cores: 4

L2 Cache (per Core): 256 KB

L3 Cache: 10 MB

Memory: 16 GB

Boot ROM Version: MP61.0116.B11

SMC Version (system): 2.20f18

Illumination Version: 1.4a6

I've ran hardware diagnostic tests with no errors coming up. Everything seems fine. Done multiples disk permission repairs and still at a loss what to do.

So basically, the computer will be working fine, and it'll suddenly come to a slow, beach ball, stop responding even when attempting to use the keyboard shortcuts to force quit applications. If audio is playing, it'll continue to play fine, the mouse will move but nothing will respond. I've got a strong suspicion that it's the graphics card causing the issue.

I currently have 3 screens connected to my computer, 2 via HDMI (1 from the HDMI output and another via a miniDP to HDMI) and one via miniDP to VGA. I've turned to looking at my computer system diagnostic logs under 'Console' but have no idea what to look out for. I'll paste a couple of lines prior to the freeze here for reference.

13/5/15 12:01:45.764 pm Dock[210]: CGSCopyDisplayUUID: Invalid display 0x0b429b86

13/5/15 12:01:47.265 pm DMProxy[3899]: AMBD Services: connection interrupted: com.apple.AmbientDisplayAgent (Connection interrupted)

13/5/15 12:02:38.059 pm com.apple.AmbientDisplayAgent[181]: AMBD Agent: xpc connection became invalid during event handler

13/5/15 12:03:13.201 pm spindump[871]: Got xpc error message in libspindump client connection: Connection invalid

13/5/15 12:03:13.208 pm loginwindow[89]: Login Window point of no return

13/5/15 12:03:13.220 pm loginwindow[89]: ERROR | -[SessionLogoutManager allPrivateProcesses] | No LS dictionary found for LSASN: LSASN:{hi=0x0;lo=0x14014}

13/5/15 12:03:13.224 pm lsuseractivityd[241]: [SFContinuityScanManager] ERROR: lost XPC connection

13/5/15 12:03:35.145 pm sessionlogoutd[3921]: DEAD_PROCESS: 89 console

13/5/15 12:03:35.156 pm mdworker[419]: (ImportBailout.Error:1325) Asked to exit for Diskarb

Would appreciate if anyone can give me directions on how to troubleshoot the issue and determine the cause of the freezes.