Hello, I have an '86 Chaparral 20' "198 c xl" deep vee cuddy. Boat weighs around (best guess) around 4k. Powered by a 5.7L, 350ci chev. with a q-jet. which is mated to a gen 1 alpha 1, turning 1.84:1 gears. I have tried an alum. 3 blade 21p (4 adults with gear and 35 us gal of fuel) and have...