90hp 2002 Yamaha intermittent power loss

[Pole-Position]

Greetings All. OK, here is a weird problem. Boat sat for far too long and carbs got gunked up, even though fule had plenty of ethanol Sta-bil in it. Took boat to dealer and had carbs cleaned and system checked over. After several uses on the bay, left the dock and hopped up on plane and got about 1/2 mile. Engine rpm dropped from 4200 to 3100 and was running very rough and eventually died altogether. Got it restarted and revved up and it smoothed out mostly. For the rest of the day, idled rough, but would hop up on plane and scoot along fine. Next couple of outings it ran ok. Next time out, did stop-n-go fishing and was fine all day, then same power loss with same rpm drop. Once off plane, would only go to 2100 rpm. Checked all connections and nothing obvious. It did eventually start running right and got back on plane. Next time, same problem. Once back on plane, while running at 4200 rpm bumped the throttle up and immediatly speed dropped to 3100. Drained the tank, replaced spin-on filter, fuel hose from filter to engine including bulb and quick disconnect, checked inline filter, spark plugs. Filled with fresh no-ethanol fuel and ran on a river for 2 hrs. Ran like new. Next day headed out in the bay and all was well until the third time moving to different fishing hole. Exact same rpm drop followed by 2100 max rpm once off plane. It never did sort itself our and limped back to the ramp. Othen than checking all the fuel connections between the tank and filter and possibly replacing the hose, what other suggestions / ideas / possibilities do you guys have to offer? I hate dropping $600+ at the dealer if it might be something relatively simple to fix. Greatly appreciate any help, and sorry for being so long winded.