Hey there, I was hoping someone might have a good idea. My main machine is a late 2013 iMac. Back when El Cap launched I upgraded only to find a huge drop in GPU performance so ended up reverting to Yosemite. Recently my hard drive failed and Apple installed a fresh copy of El Cap so I figured I'd give it another whirl with the fresh install. Yet again, terrible performance. (For example, in Yosemite, in Diablo 3, I could play on Ultra Graphics settings at full frame rate. In El Cap, even if I turn graphics settings to the lowest I can't even get past 10 or so FPS. I also experience similar problems with Photoshop. In Yosemite I could work fluidly, in El Cap I experience lag every time I try to zoom in or use the brush tool) The specs in my iMac are pretty good: 3.5 Ghz Quad-Core i7 32 Gb of Ram NVIDIA GeForce GTX 780M 4GB GDDR5 Which seems like it should handle an older game like D3 pretty easily. The part that I find most strange is that I also have a Macbook Pro from 2014 with much lower specs that doesn't even have an independent GPU (Intel Iris Graphics) and it handles gaming and photoshop without a problem on high settings. I was wondering if anyone could offer any advice on how I might address this problem?