well I had success after taking drastic measures. Mine was stuck at about 2/3rds of the way on "step 1 of 2 preparing update"
1. I pulled the plug, crossed my fingers, counted to ten and plugged it back in. The unit came right back up but of course was still not updated.
2. Selected the update software again and it went really quickly at first then stalled again at the 2/3rds point on step 1 of 2
3. Tried the other ATV in the house and it updated without issues and in about 6 minutes total time.
4. Compared what was different between the two the one that was
failing was the setting on "Sleep After". The one that was
failing was set to "Never". The one that worked was set to "5 hours"
5. Set the failing unit to the 5 hour setting and tried again and it worked without a hitch...
Why that would make a difference is beyond me
, but regardless it's working now and hopefully this info might help someone else.