backlater2,
If this rig is similar to the Chevrolet's, I would venture this guess. The oversize king pin set requires that the axle eye be reamed or machine PERFECTLY to accept the larger diameter king pin (oversize). If you have removed your existing pins, and they are not ruined, you should be able to clean up the pin and axle eye, and the pin should fit snugly in the eye...no wobble or slop. This is to test the fit..don't reuse the old pins!
The fit could be a hard palm press or light tap fit..it should not fall through, and once in, should not wiggle around.
All the rest of the bushings you get with a kit should be sized to fit into your spindles AND over the new pin.
There is a "tech-tip" dealing with this procedure. Again, I don't know how pertinent it is to GMC's.
So, to get net on your question...if the standard pin does not fit nicely in the axle eye, you should go to a oversize pin set!
Stuart
