There was never a chance that we would have been able to transport significant numbers of heavy tanks to Europe before the end of 1945 — even if the military leaders had pushed the idea (which they didn’t).
The US didn’t really have any significant tank force before 1940. We were building from scratch. And up until the end of 1943 the Sherman was better or equal to everything the Germans had — save for a handful of Tiger I’s that the Germans manage to get into Tunisia and Sicily.
I found a picture over the weekend of the Germans offloading a tank in North Africa using dockside cranes. Part of the design limits on US Tanks was crane capacity and the width of standard railroad rolling stock. There were dozens of other limiting factors.
I did not know that until recently, and I used to have a much lower opinion of the Sherman.
Apparently in early 1950s the Army wanted to shift a Pershing equipped unit from one location to another, within the state of Kentucky. It found out that there were fewer than 1,000 railroad flatcars in the entire country that could take a Pershing. That had not been a problem when the Army was taking small deliveries of new production each month in peacetime, but in WW2 the US would have had to have vast numbers of super heavy duty flatcars manufactured, and transported everywhere in the world that the Army wanted to move tanks by rail, if it had replaced the Sherman with the Pershing.
Tanks went overseas as deck cargo. The deck cranes of Liberty Ships could load and off load Shermans, but not Pershings. So the Army's ability to off load Shermans would have been restricted by the number of heavy lift cranes that had been landed and constructed.