What series GMC do you have? If it is the "fat cab", about all you can do is get one cut. If if it a regular cab, the glass was probably not cut correctly. I run a fleet of Internationals and from 1972 until mid year 2000 they used the same flat glass. We kept spares in stock. Quite often we had misfits that we had to send back. I would have a hard time believing that something happened to the cab or it was a manufacturing defect. I doubt that GM would have made a custom glass for a misfit cab.
