proper prop for 1988 spitfire with 5.0 and 20 ft long

[thoruton]

I Just traded and received a 1988 renken spitfire 20 ft length with a 5 lyrics engine. It takes forever to plane and the rpms were at 5000 at 25 MPH. I see it gas new prop and assume the wrong one was put on. It says it is a 14 in with 23 pitch and 3 blades
I am new to boating and have no idea how to figure what the correct prop is.

Help!

Thanks
Thoruton