Hello, Im a life long boater and Im guessing your problem may be with the shift cable adjustment "or" the shift linkage at the motor end make sure when your shift lever is in foreward that the shift belcrank is fully into engage position.
I'm going to have to google half of what you said, but....it's likely along the suggested troubleshooting I'm hoping to accomplish. Thank you!
I've got the motor put back together, though I'm fighting with the lower unit screws not wanting to release so I can re-fill it with oil. I've marked the hub and prop with a small diamond dremel bit, so I'll know if it slips next time I have it out.
Just need to get oil back in it and start looking at the throttle cables/assembly.