Hi Kevin
Thanks for coming back to me. I will try your suggestions re:media cache etc.
Apologies if I have been a bit close to the mark with some of my comments but it is seriously affecting my workflow and subsequently my business and hence I am frustrated. I am not only seeing issues with the white, pink, green lines etc during playback and encoding but also sluggish performance (particularly when working on largish projects - should this matter?), freezing and crashing (especially in AME when trying to render using GPU) as well as dropped frames during playback of very simple sequences. Surely this shouldn't be happening. Regardless of what you think of the new Mac Pro it is been billed as a great video editing machine and due to people like Dave Helmly telling us, in an official review of the new Mac Pro with Premiere Pro CC, just how good it all is for video editing then you'll forgive my lack of sense of humour towards your comment, especially having just invested a significant amount of money on the system.
I know that other video apps like Da Vinci Resolve are being affected but I don't use them or pay them a monthly subscription so I am turing to Adobe to sort it out. I had greatly hoped the 10.9.4 release of OSX and the 2014 release of Premiere would sort the issue but they didn't and that leaves me very unsure of what the problem is or how to fix it.
For now I will look into the steps you suggested and report back. If it does't resolve the situation then I will start a new thread to further highlight the issues I am seeing. I appreciate your help and hope we can resolve the issue. BTW, in some threads people are talking about having to send their MPs back to Apple for new GPUs due to bard vRAM - I have seen conflicting reports where some say yo do have to send it back and others that say no you don't have to send it back....who can we believe please? An official post from Adobe would be really helpful I'm sure to a lot of people.
Best regards
Alex