Thanks Theo for testing MS Streets and Trips. It was worth a try.

Guess we're back to using MapSource. It's a shame really that Garmin doesn't make a GPS model specific version of MapSource which would use the identical routing algorithms as our 550/66X series Zumos. MapSource is written for use by all Garmin models so it's not surprising that each works a little differently.

I've had some success converting Google Maps routes to Zumo routes using this website, but for really complicated routes, MapSource is still the only way to go.