[NiLuJe]

The lightning fast update process, then reboot => update process in the middle of the boot screen is the 'normal' process for sideloaded 3.X updates, so there's nothing strange there (hence the different .bin you found, the first update actually only extracts the correct .bin depending on your current FW, and makes it run on the next boot).

If you're running a vanilla kindle, an update failure like that shouldn't happen, and could be the sign of some kind of software or hardware fault. Or a really unlucky random filesystem corruption after a crash/harsh usb disconnect/plain bad luck.

You should be able to pinpoint which file is causing issues by checking the logs (on the home screen, in the search bar, type ";debugOn", then ";dumpMessages", then ";debugOff" (without the quotes), the logfile will be written in the documents folder) right after a failed update, and look for 'patch failure' or 'checksum failure' in there.

Once you know that, you *should* be able to fix it, provided you're willing to hack your Kindle, muck around a bit in the root fs over ssh, and have a sane copy of the corrupt file(s) on hand.

EDIT: I'd give you the MD5 hash of the K3G update file, but my HDD is dying, so, err, probably not a good idea ;D. There's an internal MD5 check in the update process anyway, and it's another error code than U006 (which is the basic 'uh oh, something went wrong during the update script' code ^^).