It looks like the max RPM’s is supposed to be 6000 for the Yamaha T60. What are your RPM’s currently when at WOT with a light load in calm water and wind conditions? Also, what prop and size (diameter x pitch) is on it currently?
You might already be dialed in and at maximum performance now depending on what prop your dealer put on the boat when they rigged it up new. However, if you answer a couple of the questions above, perhaps some with similar boats and motors can offer some ideas.
BTW, if it’s a new boat for you, congratulations and welcome to the forum.