I also experienced some wierd problems on my 770. However, I have an older 478 which I run along side. When they show different routes, we do a little more checking. If there does not seem to be any low bridges or other logical reasons for a different route, we go by the 478.
I do like the earlier statement that Garmin seems to be getting stupider. One thing I really don't like on the 770 is that, unless a waypoint was put in using coordinates, you cannot see the coordinates. For example, if you wanted to give the coordinates for a waypoint which does not have an address ( boondocking site) to a friend, you can't them from the GPS.