Did you check the surface condition of the synchro cone on the gear? I find they can get nicely glazed and the cones then lack real bite on the gear. Spinning it up slowly in the lathe and breaking the glaze with a very fine very flat stone does the trick. Agree that a mild bead blast to the friction surface of the ring is well worthwhile. It helps to have a few rings to choose from as sometimes the mating angles are not perfect.
Get it all right and they really bite hard. Also last a lot longer as they don't slip near as much.
Hope this helps