I am picking up a 21 Mirage plus in a couple weeks from a friend back home and will have it about a month to test with it. That will be my first step for sure. I like hearing other options since I don't get out to my boat all that often to test. Once I have the prop on the boat if for some reason it doesn't work I like being prepared to try other ideas while on the water rather then wait another month.

If your speed is gps and a good condition 23mp then your tach is off. 56 at 3900 is 0 slip. I would say you are spinning 44-4500 to get that speed at 15% slip or so