The Americans got lucky in Normandy. Unlike what Hollywood movies, where American soldiers fight off hordes of Tigers, the Yankees didn't meet any in the summer of 1944. Most of the fighting of the "big cats" fell to the British, Canadians, and Poles, but that didn't make the Americans' lives that much easier.
As unusual as it sounds, the British, whose main tank at the time was also the Sherman (mostly Sherman V and Sherman III) were much better prepared for fighting the Panthers and Tigers. By the start of the Normandy operation, the British had over 300 Sherman VC tanks, better known as the Firefly. Their 17-pounder (76 mm) guns could easily penetrate any German tank through the front. In addition to those, the British built Achilles tank destroyers, also equipped with 17-pounder guns, on the chassis of American M10 tank destroyers. In addition to all this, towed 17-pounder guns were available in ample quantities.