[Briguy]

WWp2

Since you have the closest setup perhaps you could post the part number of the yam prop and what bolt setting the motor is mounted on.

Other thing to think about is the transom on the 20 a 20" with a 25" shaft?????? Photo's would help. My best guess at 4000 rpm's you should be doing 25kts/29mph and wot 42 mph minimum.