I just purchased a gmc,4x4,crewcab, diesel, 3/4ton. My question is that when you stand at a distance and look at the rear of the truck the drivers side of the truck bed looks shifted to the right. The passenger side looks fine. I measured the box for square and it is within a 1/8". All the measurements from cab to bed are within a 1/8". The bed does seem like it sits more to the passenger side then the drivers side. But it seems with all pick-ups this is the case, the bed sits more on one side then it does the other. Could this whole thing just be an optical ollusion? I did look at some other trucks at the dealer and some seem to be straight and others seem to look like mine. Thanks for the help.

there is a little bit of room for adjustment on these i assume you have a new bodystyle duramax. there are 8 18mm bolts that hold the box down loosen them shift it where you want it and tighten them up. i think they just drop them on at the factory and tighten them where they land.

Are you sure its the bed thats crooked and not the cab? I thought the same thing on my truck until I checked out the cab mounts and one was shot. Just a thought