From the release:
With the advent of heavy German armour such as the Panther and Tiger, the standard U.S. tank destroyer, the 3? Gun Motor Carriage M10, was rapidly becoming obsolete because its main armament, the 3? M7 gun, had difficulty engaging these new tanks past 500 metres. This problem was foreseen, however, and in September 1942 American engineers had begun designing a new tank destroyer armed with the M3 90 mm gun.