Sorry to hear of all the problems you are having with the new boat, some are to be expected but it sounds like you are getting more than your share.
I agree with Rockter, revving the engine in neutral will not tell you if it is a bearing in the trans. Even disconnecting the shaft coupling might not put enough pressure on it to cause it to squeal. If it is a bearing and oil sample should show some metal in it. That might be a good next step.
SV Laurie Anne
1988 Brewer 40 Pilothouse