Answer to: MBP extremely slow after SSD Upgrade. What's wrong with my mac?Solved!! - I had almost exactly the same symptoms. SSD upgrade Super fast for a month, then suddenly became slower than ever. Symptoms included unable to keep up with keystrokes (really annoying), slow application loads, slow printing. I tried just about everything suggested on the internet; Reset PRAM, SMC, the wear levelling (TRIM). Reinstalled a clean OS (Lion, Yosemite, and El Capitan). Nothing made the slightest difference. I bought a different drive (i had a samsung EVO) I read the OWC were great...no change. Then one day the mac failed to find my hard drive. I was pretty ticked off by now. So my research for this problem went down a different road. And I ended up buying a replacement SATA cable (this one Fixed it completely---mystery solved. So if this post helps just one person avoid six months of torture I will be delighted.