1988 3.0 OMC Cobra boat jerking and falling out of gear

Hello everyone I have been having a problem with my boat jerking about every second when I put it into gear. Anything above idle the outboard portion jumps up about a half an inch every second. When this happens the sea interrupted switch seems to click as well? My first thought was the lower shift cable , but I have the red one which is the replacement cable from the black recalled one from what I understand. Next I read that the dog clutch may be slipping or even one of the gears may be missing a tooth? When I try to power through the jerk the boat just revs and the prop doesn’t even move like it is out of gear. Any help would be greatly appreciated