one of Germany's issues was that their tanks and other vehicles ran on gas and not deisel. When they overtook a Depot it was a 50/50 chance whether it would be gas or deisel and thus slowed them down.Logistics was also a huge factor which is probably derived from our mass production capabilities. The German military relied had to rely on a combination of horses and trucks for transportation, the US had so much industrial capacity that we could build lots of trucks to move our soldiers and Russia's too. Huge advantage.
Carts!
Watching Patton this weekend he stated (if you can believe hollywood's depiction) that he knew the German's were cooked when he saw that they were retreating using carts. He stated this was something he picked up on when reading about Napoleon's retreat from Moscow.