Similar story: Early 80’s, 76 3/4 ton Suburban 4X4, floor shifter with granny gears, lifted with 36” snow tires, winch. Start of Blue canyon, CHP check point, officer asked me if I would lead the last group over Donner before they closed the road. 5mph, whippers on high, 4 wheeling, stopping every 10 minutes to clear the glass, no snow tracks, drove using the snow markers on the side of the highway. Hands hurt for three days after that little trip.
It’s easy to get disoriented driving in deep fresh snow, especially at night. Good thing you had a vehicle equipped for it, and that the road was marked for the conditions.