Jumbo the front seats with the built in seat belts are from 1999 and newer full size gmc/chev extened cabs.i belive they did it that way in the extened cabs 3 door or 4 door non crewcab models was because the rear doors opened up like a sucicde door so there was no door pillar there to mount a seat belt to.as for a back seat with shoulder harness your more than likely going to have to look about 2005 and newer but not sure on that part.
thanks, lorren. the back seat with the built in seat belt is not so much of a problem, the main thing about the back seat is i'm gonna be hauling my 3 year old around in it, but i got a thing from babies r us that tightens down any lap belt, so i can put the belt through the carseat and cinch it down no sweat. i just thought it might look better if they were all the same thing. and pazz, i'm sure i've seen that in some smaller cars, but i'm drawing a blank right now.