If the boat never got to full rpm in forward than the prop is a likely culprit. When I read your original post of an engine with almost 900 hours I thought you were refering to a problem that had developed, not an ongoing issue. My bad. When we repowered Tappan Zee 3 years ago the flolks we worked with were experienced and capable. The numbers for prop size and pitch seemed likely....however we could not get up to full rpm and we had to pull the prop and repitch. Since then it has been flawless.