It's rubbish! It's just a trick - you can see the exhaust is already half missing and unsecured as it pulls up, but the low speed and extraordinarily gentle braking as he stops show how nothing is actually secured, be it body work, engine, transmission, steering or suspension, and he's having to use the transmission brake as the foot brakes aren't connected. Actually, it's pretty damned reckless to film that on a public street rather than an enclosed arena as something could easily have cuased a loss of control. Here's a more apprpriate video from the Hummer guys

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http://www.youtube.com/watch?NR=1&feature=endscreen&v=lpxoomyFs_0