so i just took my johnson 15hp short shaft to canada and put it on a 14ft aluminum standard transom. My motor pumps water great at low and high rpms in neutral. Then I take off and everything is good unitl I get on plane at full speed. Then it shoots strong for a second then sputters then real strong then sputters. I never overheated it as I always monitor my tell tale. It pumps excellent as my kicker, What do you think it is? trim it down? transom height? longer shaft?