Especially with third-party SSD drives, Enabling TRIM using something like TRIM Enabler is very important. Despite what one manufacturer says, "it can't hurt".
You will also need to run Disk Utility (Repair Disk) from a different drive that has TRIM Enabler or equivalent installed. This produces the very satisfying message: "Trimming Unused Blocks" and the program pauses for up to a minute while the junk is removed. Drive speed can increase substantially after this operation, because the drive is no longer drowning in deleted data blocks.
http://en.wikipedia.org/wiki/TRIM
The drive may need a Garbage Collection cycle to set itself right.
What sometimes happens is an SSD drive runs so low on free blocks it cannot function, and appears to go comatose. After a round (sometimes several rounds) of internal Garbage Collection, the drive has consolidated enough free space and can just barely "come back to life".
The automatic Garbage Collection inside the SSD is allowed to happen when the SSD drive is completely idle. Leave your Mac powered on, running anything (including just the Alt/Option Boot screen), but NOT accessing the SSD drive. After about 20 minutes, the drive will notice that it is idle and start garbage collection. The time may vary by manufacturer, but overnight will certainly do it.