I'd consider putting put this SSD in another desktop computer temporarily and testing it with CrystalDiskMark...
Was this a fresh install of Windows, or was Windows cloned to it, perhaps? Any other attached drives?
Alternatively, you could try another SATA port on the mainboard (if a desktop, which is unknown as you've given no other info that might often be helpful) and /or another SATA data cable (Reverse it with the DVD drive's SATA data cable if it will reach, and, swap power cables too just to rule out anything marginal there if nothing else)