Mac pro 5,1, new in mid 2013, 3.3 ghz, 6 core, 48 gb ram, 250 gb ssd boot disk, 3tb hd, 1 tb hd, mac gtx680 card. I just installed Sierra last week, and boy is it slow and laggy. I've looked up everything I could find for a fix, pram reset, smc reset, file cleaners, ect,,doesn't help. Especially noticeable opening itunes and mail, they really seem to crawl. And streaming radio on itunes just doesn't even work anymore.General internet seems ok, but everything has a lag to it, not at all snappy like El Capitan. Any ideas before I have to go back to El Capitan?