jay05elitev

Took the boat out for first time last week, runs good up to about 3200 rpm then loses power, hesitates, tach bounces, loses speed, backfires. Back off the throttle and it picks back up, no problems as long as you keep it under 3200 rpm. I have changed the fuel/water seperator filter, one can of Seafoam, ran as much of the old gas out as I could, put in 26 gals of fresh ethanol free gas and 2 more cans of sea foam, no change. Any thoughts? Maybe bad spark plugs or distributor? Boat only has about 120 hrs on it, Mercruiser Black Scorpion 330 hp motor, stock prop.