Did a little searching but couldn't find anything exactly like this problem.

Had a great long weekend on the water. Boat ran and shifted fine all weekend. Coming back into the marina I came off plane and put both drives in neutral while we threw some lines on. When I went to get going again the starboard side shifter wouldn't come out of neutral. It was extremely stiff wiggling it in to both forward and reverse. I didn't want to force it and break the cable and have it possibly stuck in gear so I docked with one engine. Got it out of the water on the forks and spun the prop by hand. Wasn't making any strange sounds and had the same resistance as the other drive. Linkage on the shift bracket looks like it's connected and wants to move on both ends when shifter is moved slightly. I haven't disconnected anything yet for testing. Lower shift cables were done this spring and it has shifted great so far.

Should I start with shifter/cables or just go ahead and pull the drive (and try to get on someone's list for service) assuming something is wrong in the upper?

2005 Sonic with twin 496HOs and Bravo X drives. Merc Zero Effort controls.

That's a strange one. We had a similar scenario happen with my buddys XR drive except it was stuck in forward gear. The cone clutch had exploded.

Sounds like the detent ball/ shift lever
or a lower cable IMO

Unfortunately had a tooth come off one of the gears in the upper and get wedged somewhere preventing shifting. I guess the good thing is that let me know there was a problem and I caught it before the rest of the gear let loose and sent material through the rest of the drive.