660 Routing algorithm

[inspiredron]

I am becoming increasingly frustrated with my nuvi 660 since updating to the latest v4.90 software. The unit's routing has become very unreliable. I normally have the unit set to Faster Time and I use the device as an aid rather than following blindly (unless I really don't know where I am going!). On almost every route o fmore than about 20 miles I find that the estimated arrival time will reduce when I use what I see as the obvious faster route where it differs from the 660's recommendation. When I depart from the 660's current route it will do its very best to get me back to it. Eventually it gives up and re-routes where I am heading and invariably the ETA gets about 15 or 20 minutes earlier than it was at the point where I first ignored the 660. The problem is exacerbated if traffic avoidance intervenes or if I take an early short cut but it is by no means confined to this. At outset I have compared ETA's from "Faster time" and "shorter distance" and have found that the ETA for shorter distance can be sooner than for faster time.
This seems to be a new problem since software v4.90 for me.
Has anyone else noticed? Or found a solution?

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