In the US Army, mechanization of antitank systems didn't begin postwar. It started with the creation of the Tank Destroyer arm. The TD people thought of their destroyers as exactly that: highly mobile antitank guns.
Curiously enough, I was just looking through that same report a moment ago.
The document is Employment of Four Tank Destroyer Battalions in the ETO, written by a committee at the Armored School at Fort Knox, and published in 1950. The committee is made up of captains and majors in a course at the school. It examines TD organization, and then examines four battalions in action.
One of these cases looks at the 704th TD Battalion, supporting the 4th Armored near Arracourt, on 19 September 1944. A platoon of the 704th rushed from the rear to cover an unguarded key position and, there, single-handedly halted a German attack, destroying fifteen enemy tanks, for the loss of three TDs (probably mobility or firepower kills rather than total losses).
The authors had this to say about the importance of maneuverability:
The conclusion of the entire report includes these thoughts:
And also:
We are talking more about mobility in an operational sense, during approach marches - about the ability to move across difficult terrain, and to pass through other units.