Seems A-OK, but...

[GT1000000]

Older tower of power, inline 6, 115HP, somewhat of a "frankenstein" motor [ different parts, different engines], that's how I got it. When I first bought it, the lower did not pump water and it was full of water. It did also have quite a bit of metal shavings stuck on the magnetic drain plug. All is well now, after replacing the water pump and re-sealing and refilling the L/U. Driveway test showed proper engagement of Forward-Nuetral-Reverse. Put it in the water, Forward-OK, good throttle response, good hole-shot, non-GPS top speed approximately 45-50 MPH, [will verify with GPS at a later date.]
Problem is with Reverse, engine goes into gear, prop can be seen underwater, spinning, but no reverse thrust. Any ideas, hints, tips, or suggestions would be appreciated.