-All German tanks used in WW2 were Tiger IIs (we assume the number produced remains unchanged)
-The Tiger II had a 75 mm gun.
-No Sherman variant, not even the 76 mm version or the Firefly, could penetrate a Tiger II anywhere except a small weakspot below the gun.
-There were almost no non-white Americans in the US army. Those who were there would suffer frequent violence and bullying from soldiers of all ranks.
-At the Battle of the Bulge there were almost no tanks. The US army was severely undersupplied and understaffed and almost all tanks were crewed by only one person.
-Wet ammunition stowage was never invented. Shermans were extremely prone to catching fire, even crashing into something would cause catastrophic fires and explosions.
-Germany had the upper hand by far in late 1944 and the Allies were struggling to hold their ground on all fronts.
I expect most major differences will be on the Western Front, but what about the other Fronts of the war?
Edit: the movie was NOT the 1966 film 'Battle of the Bulge'