Problem replacing Hitachi 250G HDD with Sandisk 250G X210 SSD

I followed the ifixit instructions to replace my hard drive with the SSD mentioned above. the physical replacement was simple. I used super duper (which I have used extensively) to clone the HDD prior to the replacement. I tested the SSD by booting the computer from it using a USB enclosure - all seemed to work fine except it was a little slow - I attributed that to the USB connection. When I physically swapped the drives and booted from the SSD it was incredibly slow (virtually unusable). Do I need a different cable since I am swapping to a SSD? Any other ideas on why the performance is so bad. the reason I was making the change was to improve the response time but it got worse. Thanks for any help