The chipset on your laptop's motherboard (Mobile Intel HM65 Express) is SATA 6Gb/s "Capable", but that does not mean that Toshiba enabled the feature in your model.
On Toshiba's website it does not indicate that your model supports SATA 6Gb/s.
CNET's review of your model shows that it is only SATA 3Gb/s (Serial ATA-300):http://www.cnet.com/laptops/toshiba-portege-r835-p81/4507-3121_7-35045556.html
Benchmark your drive with ATTO software, which uses highly compressible data to test Read/Write speeds. Highly compressible data is the easiest kind for a SSD to Read/Write.
If your Read/Write speeds are less than 300MB/s then your model definitely only supports SATA 3Gb/s.