I have a Glastron 235 GX with 5 liter injected motor. This boat used to go 48 to 52 miles an hour. But now the best I can get is 40. I change the fuel filter and spark plugs. Put in you Non-ethanol fuel. I put two bottles of fuel injector cleaner.. I have spun the prop before. But that's not the problem now. Any more help out there.