It's not worth it to disable TRIM in my opinion.

You may have mentioned this before but what SATA controller are you using again? If you have an Intel SATA II (like an ICH7-ICH10 or something) then see if that works.

I would definitely return it and get a refund and get a whole new drive, or at the very least RMA it and get a new drive of the same one to see if there is any difference.