I've done restore to default settings, and hard reset. On Garmin's recommendation I've re-installed the maps and all the updates are installed. I've checked and double checked avoidances and settings. The Traffic Trends feature is turned off, and I also clear the travel history after any long trip which Travel Trends uses for it's predictions.
I generally use MotoGoLoco for route planning and put in mumerous waypoints to try and prevent Mr Garmin from taking me away from my preferred route. MotoGoLoco which uses Google Maps generally predicts the most obvious route which looks pretty logical on the screen. But, more often than not Mr Garmin will beg to differ if there's a shitty alternative available, and in place like Wales there is usually a handy farm track near every good A road he'd prefer to use.
I'm just back from the Yorkshire Dales, North Pennines and the Lakes, and I went to great lengths to add plenty of waypoints and everything ran fairly smoothly, but closer to home where I know the roads I don't add in extra waypoints and you can see that the Zumo just wants you to divert down lanes that simply aren't the quickest / most obvious route, as in the pictures I posted above, so it does start to diminish trust in the unit.
I'm just of for a 300 mile trip to Hampshire and back with my wife, so it'll be interesting to see how we fare this time out.
Im out in Belgium and France at present and my 340 will cheerfully take me off at the first turn of a roundabout on a service road that parallels the A road , only to drop me back on the A road about 300 m further on!
Having said that it also finds some cracking routes, so I shant complain. So far Im 2000 miles into a trip and it gets me outside my accommodation every night��