Thanks for finding that video! Funny that in all the times I've been on the USH version, I've never seen the falling car work, nor seen the final Trex move through the waterfall that fast! Wonder when it was shot..,
BTW, sorry if was unclear earlier, but the first Trex at USH is the one that is just a head. The finale Trex does has legs, but its a less sophisticated animatronic that doesn't have the full-body walking animation that IoA's (theoretically) does. As you can see in this video, the waterfall is used to obscure the fact that he's a mostly static puppet that is pushed forward by a ram at the last moment; in IoA he has a whole warmup animation cycle while you approach that is more dramatic (though less shocking) if and when it works...