2350 rsr

I have a 2016 (bought new) 2350 RSR boat with a WOT speed of 32 MPH (measured with a GPS) and an RPM of 5550.  Everything I read says my prop is close to ideal and I should be getting between 38 and 41 MPH.  Any idea what is wrong?  The dealer has not been very helpful.  For the tech info...