Last things first, I'm not 100% certain how the Active KillDisk program works, but if it actually did write '0' to the entire SSD, that is not clearing or secure erasing a SSD. Actually, filling any SSD with '0' fill is not a good thing at all.
Writing to the NAND chips in a SSD does not reset it to a fresh state, it does exactly the opposite. NAND storage cells must be "erased", which means they are in a ready to be written to state. When NAND cells have been written to, regardless of what was written, they must be first erased before written to again. With all the NAND cells in a SSD in the written to state, the SSD's response is slower when trying to write to them again, since an erase must be done before a write. The SSD's firmware may not know that the data ('0's) are unwanted, garbage data, and may try to preserve it, further slowing down its operation.
The SSD Toolbox Secure Erase option would be the correct method of refreshing your SSD. Other than that, performing a quick format of the SSD on another PC running Windows 7, and then using the Toolbox SSD Optimizer on that SSD would be the next best option.
But checking the SSD with the Error Checking feature, and recording the results before calling Intel support, will be the first step before an RMA.