The newer model ones, with the separate plastic oil tank, have built in filters/screens made into the tanks. After a while, those screens get stopped up and P/S systems starve for fluid on intake side and at high RPM’s the excess fluid have a tendency on escaping past the fill cap on return side. Replacing the semi-clear P/S tank fixes that problem.
If you are talking about an older model (with metal tank/can), then this does not apply.
It happened in my 79 on my way down Route 55 at about 65 mph with the big gear 4:30 she screamed but held at 200 degrees. I think the pump was just over spinning