Last spring we ran the TET-S going the other direction and I used a Nuvi 550.
FWIW If you run the route as an offroad route, it does not screw up the calcs like it does if you try to make it road route.
In fact I found it worked really well running as an offroad route.
We got to FS205 coming from the other direction, and I got concerned that it was going to be a dead end as the garmin road stops, but as you know it doesn't.
Also coming from the other direction, there were private road/no trespassing signs on the road leading up to FS 205.