Garmin got stubborn

I don't know the details of your unit. but my Garmin 660 allows tuning of the route. At the simplest it's e.g. FASTEST, SHORTEST, SCENIC or some such thing. On my Garmin you can tell it to avoid toll roads, ferries, U-turns, etc etc. You may have something in your configuration that's forcing your route 'off track". Your current performance sounds very much like the "NAV" system in my Chev which is totally useless.

I always have my Garmin in the truck as well. The only silly thing it does is often it tries to make me exit an expressway then immediately get back on. Through Toronto it will try that at least 10 times.