How fast can an North American antelope run?

You're likely thinking of the Pronghorn, which is often called the "North American Antelope".

Pronghorns are incredibly fast, reaching speeds of up to 55 miles per hour (88 km/h) in short bursts. They can sustain speeds of around 35 miles per hour (56 km/h) for several miles.

This makes them the fastest land mammal in North America, and actually, the fastest land mammal in the Western Hemisphere.