Part of the situation was Army Ground Forces doctrine. Tanks were vehicles of exploitation. They were to play the role of horse cavalry. Tank to tank warfare was to be the domain for the tank destroyer force. The Pershing was a not ready for early 1944 manufacture. Consideration was given to replacing the Sherman with the T 20 series. These tanks had the lower silhouette of the Pershing but carried the same armament as the 75mm and 76mm Shermans. The Shermans proved ideal for the open warfare of July, Aug and early Sept 44, and combined with the Jabos of the 9th AF their results would not have been improved upon had they been replaced with half as many Pershings.It was true that in tank to tank battles US tankers were ata disadvantage, but in infantry combat US troops were also at disadvantage given the quality and numbers of the MG42 which all but negated any advantage of the Garand over the Mauser. What really gave US forces a solid advantage was the superiority of its artillery. In terms of its quality, numbers and time on target doctrine it was the King of the battlefield from the earliest days at Kasserine to the very end.
True. That doctrine was part of the debate between wars between the traditional three branches of the Army, Infantry, Cavalry and Artillery, each of which claimed the tank should be dedicated to them.
The Infantry wanted it to be a support vehicle. They wanted a heavy, wide tracked tank with a long, high velicity gun for destroying bunkers and enemy tanks. They didn't care about speed, as they claimed it didn't need to go faster than the infantry.
The Artillery considered anyting with a cannon to be theirs, and viewed tanks as mobile artilery. They objected to any long, high velocity gun, as they burned out barrels faster. They insisted that a barrel should last at least 1,000 rounds. According Belton, it's doubtful any tanks lasted long enough in combat to ever fire a thousand rounds.
Finally there was the Cavalry. With horses obsolete, the clear answer for cavalry officers like Patton was the tank. They wanted light fast tanks to fill the cavalry role. Although they won the argument in terms of doctrine, the M4 was a compromiise; light and fast, but with a low velocity gun the artillery favored.