Only one can drive the pickup at a time, so what are the other two driving?

I'd figure the real cowboy would have to be the one driving the pickup. My reasoning is if it were a horse, then the real cowboy would be the one holding the reins. Real cowboys ain't doubled up in the saddle since the days of the Knights Templar, unless you figure they're being chased by the posse or a jealous husband, and one of them lost their mount while trying to get away. So the one holding the reins(or in this case at the wheel) has to be the real one, and the other two are just tenderfeet along for the ride.

Of course you could also say that no real cowboy would be using a pickup unless their horse was down, so then that'd make the one riding shotgun the real cowboy (everyone knows no real cowboy is gonna be the pivot man), and he's just catching a ride back to the ranch. He wouldn't ride in the bed because his hat would blow off in the wind, so he gets the window seat so he can roll and smoke or chew and spit without having to reach around someone to get to the window.