Hmm.
Here's what.
It needs to have less curves, make it more like the standard Jeep.
Also, flatshade it.
Also also: I'll script it for you, if you want.
Also also also: I don't know how to package addons, so I can't do that.
EDIT: Also also also also: There's probably something wrong with the collision model for the wheels, but I'm no expert.