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Michael
Sounds to me like that is a cartography problem, rather than a Garmin programming problem....my Nuvi at that time wanted to route me through Newark, and later kept insisting that i take a state route that either did not exist or was not marked on the roads.
Garmin makes the hardware, and also the software that operates the device, but they don't make or modify or inspect the cartography (maps) that are used on their devices. For many years, Garmin products used Navteq cartography. Navteq, a totally independent company, creates their maps from a combination of sources - government produced maps, their own research, and other commercial map suppliers.
More recently (last 2 to 3 years), Garmin has switched away from Navteq and is now using maps created by HERE. HERE is owned by Noika, who I think have recently been purchased by Microsoft. There are some advantages to the change to HERE cartography, most notably that HERE permits 4 map updates per year (every 90 days) for users who have lifetime subscriptions. But, due to changes in the way the map data is compiled, only Garmin hardware that is less than 2 to 3 years old can take advantage of the quarterly updates. Older Garmin units with lifetime subscriptions get 2 updates per year.
Anyway, getting back to your routing problem, my guess is that it was caused by an inappropriate road attribute (speed limit, road classification, continuity problem, etc.) being set in the cartography for the most desirable route. As a result, the navigator looked for the 'next best' route, and that is what you got. Those kind of errors normally don't persist for more than one update cycle, because users report the errors back to Garmin, and Garmin passes the reports back to the cartography supplier. It is also possible that the strange routing may have been caused by a user-selectable preference that you had enabled, for example, 'no toll roads', or 'avoid expressways', or similar. If you have a traffic device attached and enabled, the routing problem may also have been caused by an inappropriate traffic report that listed the road as either closed or congested.
Michael