The X25-M G2 Intel SSDs have two firmware versions, the original is 2CV102HD, and the update as you know is 2CV102M3. Since the firmware you are interested in was not an update, it was never supplied in any update tool or as an individual file. So the chances of finding it, or even a way to change to it are zero IMO.
Your X58 board uses the Intel ICH10R SATA II chipset, which was a very well respected product, I've used several boards that had it and never had problems with it. As long as you are certain you are in AHCI mode now, you could try the following:
Check or replace the data cable, with replacing it the best option. Also check the power connection, as in removing the connector from the SSD and reinserting it.
The SSD Toolbox has two Diagnostic tests, you might as well run them and see if any problems have occurred.
A much more work intensive option it to secure erase the SSD with the Toolbox. That will COMPLETELY ERASE the contents of the drive, NEVER to be retrieved again!! You would need to back up the SSD completely, and restore it after the secure erase.
Ask yourself, are you absolutely certain that your issues started after the firmware update, and there was nothing else you did to the PC that might have caused it? An easy thing to overlook, I've done it many times.
Personally, I've used and still use several of the 80GB version of your SSD, with the new firmware, which has been available for going on two years, and they work fine. Your SSD may have other problems, and you can contact Intel support directly via the Support link at the bottom of this page.