Bought a 19' javlin bassboat with a 150hp outboard, it would top out at 56mph when i first took it out. now im only getting 46mph and the prop felt like it was slipping sometimes when running top speed.

took the SS prop with a 23" pitch off and a friend gave me an Alum. prop with a 19" pitch, put it on and still running 46mph at full throttle. I also have a GPS and it says 46mph also.

Think this 150hp outboard motor should run faster than 46mph even with the Alum. prop, any ideas why im not getting the speed i should? Thanks for any info.