I just bought a '79 1/2 ton 4X4 short wide box and the cab is sagging on the drivers side. If you look at it from the front you can see a drop of about 3 inches. The bed is still level, it is just the cab. If you look through the rear window you can see just how much it saggs by the window trim of the canopy. Any ideas or sugggestions on what the problem is and a fix.