Ratmins

New to this but here goes:
My tranny is shifting eratic. If I put my boat behind it seems like it looses power and shifting gets even worse. Had the tranny rebuilt last year. It's had speed sensor replaced pryer to that. No new codes showing but past codes show PO608 and PO609. My mechanic has spent 3 hrs trying to trace problem but said I should take to dealer and see if their test equipment can trace it down better than his. He did tell me the PCM is not the factory installed one, it is remanufactured. He said could be PCM or maybe wiring and did disconnect and clean harness to PCM. Hope someone has had the same problem and can shed some light on the issue.