1999 Tracker pro series by mercury 90hp 2-stroke shifting problems

[District2lt607]

I have a 99 Tracker pro series outboard by mercury. Initially when i would shift from neurtral to reverse, I could hear the transition but it wouldn't engage. It acted like it was still in neutral. Motor would rev but prop wouldn't turn. It worked more often than not. Then yesterday it happened in both forward and reverse and doesn't work. RPM's will race, but prop doesn't turn. I can't hear or feel the transition between gears anymore and shifting is easy. Cables, linkage, and all under the cowl LOOKS to be moving and operating properly. What should I check next??