Have a 1978 Sea Star Spoiler deep V 888 18 footer with inline 6cyl engine. 2,200 lb empty weight. Engine was new about 6 yrs ago, 3 yrs before we got it. Runs very nice, but with the 15 X 19 aluminum prop WOT revs would reach upper 5,000's and supposed to be ~ 4,300-4,500 per manual. Got a 21...