You can force TRIM by booting into single user mode command prompt and run fsck with the right options. Your SSD must show up as TRIM support YES. if not use TRIM Enabler.
Here is how to:
1. Switch on your MacBook
2. Hold COMMAND and S key simultaneously
3. Once you arrive at the command prompt type: fsck -ffy
4. During the last step of fsck you will recognize a message that says "trimming unused blocks". Depending on the state of you SSD that takes anywhere from a few seconds up to a minute or so.