I have a 1990 374V Ranger with a 150hp Johnson Fastrike with a 24" Raker I had cup added by Mark Croxton and I also have vent plug holes, when I take off the motor revs to about 3500 then seems to break loose to about 4700rpms then seems to catch again then I start trimming up, should I add a smaller vent plug to stop this or leave as is top rpms are 5500rpms and about 57 to 58 mph no jackplate thanks