Like he said "Turn off 'recalculation' in the GPS.  It's bad at it.  If you miss a turn, sort it out yourself.  It's usually easy enough to do.  In extreme cases stop, zoom out the map until you can see your route, then ride to it."

Spot on Mark.  After 3 months of frustration with my new Garmin 1000 I was beginning to wonder if I had bought a dud device.  So, your comment makes great sense to me and raises the question "why does a market leading company such as Garmin offer services that it cannot provide?"