I dunno. I watched that truck driver that got pulled out of his truck at the start of the Los Angeles riots get seriously beaten for doing absolutely nothing. Being a Christian doesn't mean we have to be doormats. My truck is not only my living, but many times I have several thousands of dollars in customer's cash in it that isn't mine to lose. I'll go with hitting the gas if I can do it (if no other cars are blocking me.) If I can't get away then I'll do what I have to in order to stop the guy. Not a good idea to bring a knife to a... well, nevermind.
Oh, and if he had a gun, I'd turn toward whatever side of the truck he was on and hit the gas (assuming no one else is in the way). It's actually harder to shoot a close moving target than a far one. If I hit him fine, but even if not, by the time he gets his balance and aim back, I'll be to far enough away for safety. If there are others in the way, well, at least I didn't bring a knife to a...