Yeah me too it’s driving me nutz!!! Very simple composition, even with all FX off and a single layer of footage only it still will only playback RAM previews at around 17 fps, with the audio WAY out of sync! I try Shit-RAm with 1 skip frame which sometimes works but not often. I’ve configured everything as per specs and am using CS6 on a brand new 3.7 GHz Quad-Core Intel Xeon E5 Mac Pro. Used to work fine on my iMac at home, also fairly new, maybe 18 month old highest spec model available. I’m doing work which really does need very careful attention to audio cues and I’m losing my mind here… PLEASE CAN ANYONE SHED SOME LIGHT ON THIS??? Only difference i can think of is that the newer machine is running Yosemite, but the machine at home is running Mavericks? I’m dying here… Oh hey I just thought of something, I’m running two 4k Samsung 28″ monitors via the thunderbolt ports on the new Mac Pro… Is that something that might affect things? Hope not…