I need some prop advice

[Tenntrapper]

I have a 1548 with a new Yamaha F25 4-stroke. This is my first 4-stroke motor, and it's completely different than the 2-strokes I'm used to. All of the power seems to be on the low end. At less than a quarter throttle, it planes out and runs 21-22 mph (gps). However, I've finally been able to go wide open (breaking in new motor), and it tops out at 26-27mph. It came with a 11.25" pitch prop, and I've found props up to 15". I don't want/need a half dozen props, so I guess my question is, can someone with a similar set up suggest a starting point? I don't want to kill the bottom end, but it's almost flat above about half throttle.The rpms do go up, just very little gain. Or am I looking at this wrong, and 4-strokes are supposed to only be run at quarter throttle? Thanks for any help.

 

[Tenntrapper]

Just wanted to update my own post. Found out the issue with the boat. It's with the boat itself. The G3 has welded in trim tabs. At a given speed, it lifts the back of the boat and plows the front down into the water. Maybe I need more weight in the back.