Original post by: Dan ,
I would start by checking the systems firmware. Follow this Apple T/N: [https://support.apple.com/en-us/HT201518|About EFI and SMC firmware updates for Intel-based Mac computers]. If it's newer that whats listed here you're OK. Makes sure the SSD's firmware is also upto date. Did you enable TRIM services? The next thing here is reformatting the disk as you replaced the SATA cable you should have done this. That way any errors on the drive doesn't mess you up. In addition, it would also verify the cable was good which still could be an issue. I add some tape around the folds to give the cable some additional protection. Also make sure the rubber grommets are present on all four mount points. The last thing here is making sure the drive has free space. You should have 1/4 to 1/3 of the drive free (smaller drives need more space). Also clean out the old cache & logo files. Here's a good tool on the App Store to make this easy: [https://itunes.apple.com/us/app/disk-doctor/id455970963?mt=12|Disk Doctor]. Let us know what you find.