He ate really big, bulky prey, and they didn't live in the jungle either. The king of the tyrant lizards probably lived in open terrain, or along the edge of forested areas, as did the critters he fed on.

And we don't even know for sure if he was a predator. There is good evidence to show that he ate carrion, which would require little in the way of speed or maneuverability in broken terrain. There must have been a lot of big, dead plant eater corpses littering the landscape. Indeed, some recent research seems to show his leg musculature and bones could not support an agile, mobile predator; certainly not in forested terrain. If he was a predator on live flesh, perhaps he was an ambush predator, haunting waterholes and other such places where his prey had to come to him.

Two legged predators generally today (such as most birds) feed on prey much smaller than themselves, and they sneak up on on it, such as herons and egrets. The only large bipedal predator I can think of today were the big extinct birds like the New Zealand moas, or some of the big predatory land birds of the post-dinosaur era.

We don't really know the answer to my question, but I think we're missing something. All we know for sure is that T. Rex ate huge mouthfuls of meat, as evidenced by his jaws and dentition. Other than that, we just don't know.