[RedDevil]

I think the flashers did it.
Other vintage cars don't do that well either on such a grade, and loaded semis would be very much slower.
I made a trip around the national parks in '87 in a 2.3 liter Ford Tempo with a 3 speed auto. It couldn't hold 3rd gear on those grades, and sunk below 45 mph in second as it did not rev that well. So we had the occasional row of cars behind us. Luckily everyone was patient and once they got past many showed their compassion with a finger.

I did own an '86 Diesel Rabbit, 4 speed manual. How I cursed it for not having a 5th gear. But it had a tow hook.
One day I hired a trailer to move some cupboards to my inlaws in Zeeland. Driving against a storm, it could not hold 4th gear on the flat. I drove the freeways (up to 120 km/h limit at the time) at barely 80 km/h (50 mph), oil temp needle at the edge of the danger zone.
In Zeeland's 2 lane no passing road a long line formed behind me. Then at ascending the Zeeland bridge even 3rd gear did not cut it any more, I had to shift to 2nd oil temp light flashing and all. I finally managed to touch the 80 km/h speed limit on the down ramp 5 kilometers further... That was an experience I promised myself to avoid from then on.