My 88 40 HP VSO is cutting out and losing power when it is close to or over 4000RPM, usually with-in a minute of my setting it there. It runs perfectly fine at 3500 and below. I have changed the fuel filter, tightened all fuel hose connections, substituted a different fuel tank (both portable) drained both carb fuel bowls. Does this sound like a fuel pump problem? If so is it rebuiltable or must it re-replaced. Anything else I should be looking at?