I have the exact same model boat, same engine with 4v carb. Bought it new and it has original aluminum prop. Mine trims out at 5200 rpm and a little over 52 mph on normal water. With just me onboard and smooth water it will hit 55. I've verified it with a gps and it's within 2 mph accurate. I usually run 4500 rpm cruising at approximately 45 mph.
I suggest you first verify the prop is the same as what came from the factory. If it is not, I'd go to that. My boat comes up on plane very fast and runs great with the factory prop. I let a guy talk me into trying a ss prop 2 years ago, same pitch and size as mine. It topped out the same but was slow to come up on plane. So I stick with the aluminum. Plus, I have a lot of stumps in my lake. I'd rather break a cheap prop than an expensive outdrive.
If your prop is the same as factory, start checking that engine. Check compression, then spark, then fuel. When was the last time you changed plugs? Also make sure the throttle linkage is set properly and not binded somewhere. Make sure the auto choke is not sticking, that will knock off a lot of rpm's.
One thing for sure, your boat should perform just like mine.
