If you have endshake on the yoke itself, perhaps the crowned screws in the sideplate got switched. In the older design, the screw in the sideplate that secures the yoke was fit to the yoke button as the previous poster has stated. If they get switched, this can cause the out of spec condition you describe. If you have an older model 29, made before they introduced the new spring loaded plunger screw on the yoke, try switching the "crowned" sideplate screws.
Another option would be to install yoke/cylinder shims to repair the endshake condition. Very simple intervention that can restore the proper gauge both on the yoke and the cylinder.