I have a mid 2011 27" imac. Intel i5 20GB of RAM 1TB SATA Hard Drive OSX El Capitan. It is running very slowly. When shut down it takes a while to startup. Usually I can press the power button go get a drink and come back and it's still loading. Also once it's started up and logged in it takes a little while to first open programs. The rainbow spinner appears pretty much every time a program is opened. Usually once a program is opened for a minute or so it will run fine. I have clear out a bunch of files leaving the hard drive only about 25-30% full. I have cleared the caches. I have tried an SMC and PRAM reset. It also takes a little bit of time to shut down. It will go to a black screen and just show a spinner a little bit before shutting down. Is there anything else I should try? I have plan to take it into Apple if it doesn't improve but the closest Apple store is 3 hours away so I only go there once a month. I'm wanting to try anything that might help before taking it down to them. Thank you for any and all help.