The Stiletto SS 3 blade 19X17.5 on my 5.0 Mercruiser/Alpha 1 WOT is
4600. 6,000 lb 25' boat. It has been o/hauled twice in 16 years; picked
up 150 RPM from the slight change in blade profile. I'd say your motor
is not performing up to snuff, or possibly the Gear ratio in the
outdrive is wrong... Plenty of C.I. to run your original prop at 4500+,
unless the props a dog and not designed well. (probable).

The bluewater is known for being a pig out of the hole, and incredably stern
heavy.

The engine is running as good as it's going to w/o a rebuild.
No blow by, even compression. New plugs, wires, cap/rotor. Timing set. New
coil (really helped a lot) and a professional carb rebuild.

The original prop was a 17 pitch; the PO got a "deal" on this 3 blade SS prop
(19 pitch) on the hope that he would get a higher top end.

Thanks
-josh