This is true. When I was in the crawling world, a small group of us did a moab/CO trip. One of the guys with us had a mildly built jeep and had wheeled with us a lot around TX. He gets up in the elevation and off the pavement and he lost it. He fell way behind, I hiked back up the hill to see what's up. He is physically locked up, with his foot hard on the brakes, hands on the steering wheel and wouldn't look away from straight ahead as I was talking to him. This was on a wide open slightly slanted area, maybe 5-7 degrees.
My wife ended up driving mine the rest of the way down, I drove his rig and he walked. He left back for TX that afternoon. After we made it back home, he calls and offers his jeep to me at a ridiculously low price, he was done.