At km 4 you should have turned towards Coffrane and just where the train crosses gone left up through the woods and when you get out take a left again and climb past the farm houses to where that dirt road you were looking for went off to the left again.
Still impressive how you climbed and climbed.
Actually, I looked at my track from when I did this with Lucia and I was right yesterday, I just should have kept going a bit longer on the same road and I would have reached the plateau. Will do it again soon!