How about instead of sliding back on rails, which would be tough with the bed/cab mating, have some different hinges where the door unlatches, pops off the cab 6" or so, then hinges back...
It's tough to explain...
Actually, just imagine the door LOOKING like the action a sliding door on a minivan uses, but use multi-point hinges to do it, instead of rollers and rails...
It would probably take up a lot of inner door panel space though.
Nick