In addition, my mainboard only has ICH8 chipset, and offically it does not support the AHCI, however I can change my sata mode to AHCI in the BIOS, and of course my Windows 7 ultimate 64 bit is running my SSD on AHCI mode now ! This is so confusing
It is getting slow because you have filled it up. You need to get some files off of it and free some space up. AS all ssd's will decrease in speed once they are filled up.
Its not confusing your mainboard supports AHCI....just not on the Intel ports...but AHCI would not help you.
When I had intel P965 chipset (ICH8R+AHCI+WIN7), I had to run intel toolbox twice a week.
If SSD was still slow, I delete all windows "system restore points", then run intel toolbox again.
If that does not fix it, do what KILLER_K said and run tool box again.
I now have intel P55 chipset (ICH10+AHCI+WIN7) and I also have to do the same thing (if SSD gets full and/or slow), but now I don't need to run intel tooldbox anymore.