Ok, of it's not a cable connection issue,
1. is the cable itself in good condition?...
2. The only possible change you can get with updated drivers and BIOS is improved usage of your hardware, which translates to better usage of the power it's getting. So, I'd guess either a power issue may be in the works... or a lose GPU, dusty PCIe slot, PSU issue.
3. SSD speeds all over may also indicate a power issue due to PSU issue, or maybe the SSD itself. Has the boot time remained the same or changed?
4. A BIOS update may be changing a SATA Controller setting change.
See if any of these suggestions make a difference:
• Reset the Graphics Card,
• Clean the PCIe slot
• Try a different PSU
• Try a different SATA port
• Try a different SATA cable
• Try a different SATA controller setting in the BIOS
• You can try Hard Disk Sentinel. The S.M.A.R.T. report will tell you the condidtion of your SSD reporting a Bad Block count
http://www.hdsentinel.com
• Basically any decent SMART tool will do.
http://crystalmark.info/software/CrystalDiskInfo/index-e.html
• Intel for example offer their own tool
http://www.intel.com/support/go/ssdtoolbox/
• The SSD drive manufacturer should give you SSD toolbox to check it.
• You can try CHKDSK on SSD but use it to repair system files not to fix bad sectors.