general problems of the 2003 GMC Sierra

2003 GMC Sierra 2500hd crew cab cloth split bench: the shoulder harness seatbelts on all three passenger seats will lock up during normal cruise (no sudden stops or yanks on the belts), and will continue to get tighter and tighter until the occupant must unbuckle the seatbelt and let it completely retract before it can be re-buckled. This will occur on nearly every trip in the vehicle, and has occurred since it was new. This is more than an annoyance, it is a safety hazard since the passengers must unbuckle their seat belts in a moving vehicle. The dealer (jim waldron GMC, davison mi) claims it is simply a design flaw and they can do nothing to correct it. They say that "everyone" with a 2003 Sierra is complaining about it. This problem never occurs on the driver side seat belt. I am seriously concerned for the safety of my passengers in this vehicle that is designed to carry many passengers.