Motor Issues

We are experiencing motor troubles. We were on the water today cruising on plane, about 10 minutes on plane, the motor RPMs went down and the boat came of plane without change in throttle. We reset to neutral and tried throttling up again. RPMs began rising and then all forward thrust is lost and go back to idling. Tried this over the course of the 40 minutes it took to get back to dock. Everytime motor seemed to peak at RPMs but with no change in forward thrust. Every couple times motor would catch and thrust would pick up, but then seconds later forward momentum would slow. When motor is idling, motor runs fine, very smooth. In reverse motor runs fine, very smooth. In forward, motors runs rough and feels like something in the lower boot or prop is grinding or not catching correctly. You can hear/feel a grinding/catching in the motor and in the boat. We took this to a repair shop, said there was a problem with the hub in the prob and that they switched the hub and prob. Obviously that was not the issue. We took the "new" prop off ouselves and all the gearing and equipment within the prop and shaft looks 100%. Any help would be appreciated.
Brandon from Texas

Hello Brandon from Texas,welcome!!Drain oil from lower unit and see if there is metal shavings .When you take out the screw it has a magnet on the end of it and it will have metal shavings on it.A little bit is normal,but alot is no good.Let me know somthing and i will try to help you!!Also you may have wrong prop.

Hypothetically, say there were shavings, what issues would cause a problem of this sort. Would the problem be at the drive shaft and the prop pin?

Slipping prop hub.

Jeff