Human intelligence is a fickle thing rumours might end up being almost completely wrong, or pretty much right on the money. For instance, this interrogation resulted in information that ends up being almost correct, but it's hard to filter out what is wrong and what is right from this piece of info alone.
"To the question of what new types of tanks the prisoner of war saw, he replied that he saw no new types of tanks, but heard that German tank industry began production of new types of tanks: the T-V with a powerful engine, high top speed, a mass of about 36 tons, and armament of one 88 mm gun and two machineguns, as well as a T-Va tank, which had a 105 mm gun and two machineguns. In addition, he heard about the "Dikker" assault gun, with a powerful engine, good mobility, and mass of 36 tons."
This interrogation took place on August 9th, 1942, so a new tank with an 88 mm gun and two machineguns was indeed about to go into action on the Eastern Front, the Tiger tank. The T-Va and "Dikker" are probably the Pz.Sfl.IVa, which indeed was an assault gun with a 105 mm cannon, but it's hard to call its engine powerful or mobility good. Its weight was also considerably less than 36 tons, while the Tiger weighed considerably more.