The USA Pershing M-26 Tank was one of the best tanks in WWII. It became operational in 1945 and went on serving during the Korean war.
With the Sherman Tank the USA made a choice for quantity instead of quality. But in the war in Europe in 1944 it was clear the Sherman could not keep up with the Panther and Tiger tanks. The Pershing tank was heavy armoured and had a 90 mm gun.
Actually, your design is very very similar to Nathan Elkins's pershing. Take a look at his pershing, your turret design is almost the same as his turret, and same for the body as well, just without the side shield. His website is http://www.moc-pages.com/moc.php/329900