I worked on a F550 a couple summers ago, had a crane, service body, etc. etc.
Manual trans, had it in 2nd or 3rd going up a slight hill, pedal right on the boards, would barely pull itself. Getting back to the shop, she didn't really wanna stop.
Was there for a commercial vehicle inspection, and my boss told me I needed to reline all the brakes, front and back, because they were glazed and that's why it wouldn't stop.
No, I think it won't stop because it's probably 10,000lbs over the GVWR.... LOL
New pads, rotors front and back...and there it is. Still stopping....eventually.... NO better than before. That was a spooky ride. They parked it not long after that.
Today I finished up a 2014 Super Snake. 1000hp car, finished up the brakes and the other guy I work with finished up the supercharger install. It's an EXACT copy of another car we built, the guy got another one for his wife. Then started on an engine/trans assembly for a Cobra kit car, the roller should be at the shop by the time I write this, for the engine and trans tomorrow. Aluminum body on this one.