This has been a major issue for me. Whenever I travel somewhere I don't know I do a reality check via google on my computer at home before I leave. The last 2 times I used the Tesla nav it started out with the exact route I came up with. Then it changed en-route! It was absolutely insane and WRONG. In one case the route had me circling into my destination - round and round until I got there. Yesterday it wanted to re-route me onto a freeway that was a LONG way off from my route telling me to travel on that freeway away from my destination the U-turn and head back. It seemed like a bad joke. On top of that the voice was telling me to get onto a different freeway than was stated on the written/text instructions. This thing is really screwed up and I'm thinking about getting a gps unit. Bummer.
* It continuously reevaluates the route as one travels it, and posts new routes whenever it computed an advantage, causing the distance and ETA to fluctuate wildly. Why not ask for approval for a proposed route and lock it in when approval is given? If approval is not given, why not ask what criteria apply? Minimum time, minimum distance, toll free, other?