When you say you have the correct prop, we realize that the prop is intended for that outdrive. It fits and it's correct. HOWEVER, there are props that fit your outdrive that are pitched differently. You have a 19 pitch prop. The pitch is the angle of the blades. a 19 pitch prop should propel the boat forward 19" with each revolution. That's what the pitch is. There are hundreds of propellers out there that will fit your outdrive. There are quite a few different pitch of props for your boat. I have several for my boat. The one I use the most is a 17 pitch aluminum prop. It will get my boat on plane quickly and will run my boat at about 40 MPH at about 5500 RPM. If I'm heading on a long boat ride, where I won't be stopping an starting, but will be on plane and running at higher speeds, I use my stainless 19 pitch propeller. My boat will go 45 MPH at 4700 RPM. When I use to pull skiers and tubers, I used a 16 pitch stainless prop. My boat would go 37 MPH at 5300 RPM, but got on plane very quickly and had a strong take off or "hole shot". All of these props were correct for my motor, but all served different functions for me. We don't have transmissions on our boats. We have one speed. One of my props is like running in first gear, another more like second gear, and the third is like putting it in overdrive. A prop that is pitched too high will theoretically give you higher speed at lower RPM's, where a lower pitch will require higher RPM's to reach the same speed - if it's possible. If the pitch is too high, your motor will not be able to turn it as quickly, so speed will suffer and your motor will be bogged down. Like trying to start off in 4th gear on a stick shift car. This is why we need to know your RPM's and speed.
We are sincerely trying to help.
