If the forced guide data purge doesnt fix the issue, then its probably a bad unit, and will need to be replaced by DirecTv. Constant reboots, even with the original software, wasnt one of the bugs I can recall being reported a lot.
You can always perform a power on self test (hit SELECT) when the checking system screen pops up during bootup, run the short tests, and see if you get any errors. I wouldnt run the long hard drive tests tho, as they take a LONG time.