Propellors
 

I JUST REPOWERED MY 37 MIDNIGHT WITH 575 600HP NA FROM 540 550HP NA. THE BOAT HAS BEEN LAID UP FOR A FEW YEARS. MY OLD PROPS WERE 26 X 17 3 BLADES ACHIEVING 74MPH WOT.
MY NEW PROPS ARE USED 27 X 16 3 BLADE, I AM UNABLE TO GO BEYOND 5000 RPM AND LESS THAN 74 MPH. THIS PROP FEELS MORE SLUGGISH OUT OF THE HOLE VERSUS MY OLD PROPS WHICH I DO NOT HAVE ANYMORE TO INTERCHANGE. MY QUESTION IS CAN A PROP LOOK GOOD AND BE BAD,RESTRICTING TOP RPM AND MAYBE INCREASING FUEL CONSUMPTION. I GOT MORE HP ,BIGGER PROPS AND LESS SPEED ?????

If you didn't increase power I wouldn't expect any speed increase from just props.

You may not have enough HP at 5000 rpm to get over the hump to where your new engine makes max HP/ torque. Did you put in a larger cam?