I Just purchased a 2004 246 JC Tritoon, it has a 225 hp Evinrude direct injection, Model E225FPL SRB, it has a 14.1 x19 ss prop on now it runns out at 5800 rpm and 35 mph with 2 of us in the boat. Is there a prop I can put on that will lower the rpm 3-400 rpm but give me a speed in the lower 40s
RPM-wise your rpms are pretty good on a pontoon boat. The revs will drop as you bring people and gear onboard and when the weather gets very hot and muggy.
Gaining 5mph with just a prop change may not be possible and you could not carry a load of people. A 17" Rebel or a 19" Viper are possibilities for some speed improvement but whatever you gain will be offset by what you will lose at the bottom end. Don't forget to try raising the engine for less drag. Everything will be trial and error.
A pontoon boat should be propped at the very top of the operating range with a light load for all around usage.