I originally ran a battery of stress tests, from Linx, to P95, to memtest86+ for many hours and they all turned out fine with a vcore of 1.2625, but over the past month or two I started getting errors in Linx after an hour, so I bumped it to 1.27 and it ran fine. Then it got errors with 1.27 so I had to bump it to 1.28, and now it won't run with 1.28 without getting errors.
I ran memtest86+ yesterday for 17 hours and 11 passes and it came out with ZERO errors.
I've had the same bios settings and no hardware has been added since (unless you count switching monitors).
Otherwise send it back to Intel. From what I saw somewhere on here Intel has no way of knowing if the chip was overclocked since overclocks are stored in the BIOS on your motherboard.