Recently purchased 2003 Nitro 1900 tunnel hull with a Mercury 90 hp 4 stroke mounted on a 6" jackplate -- according to previous owner boat has always had issues getting on plane. Current prop is 13x19, three blade. Engine at 4000 rpm (~20mph) will get boat on plane -- take a long time. The motor is all the down on the jackplate which I feel is too low. What's a good starting point for adjusting the motor height, 4" below the tunnel on the lowest point on the hull? Thinking of going to a 4 blade, 13.4x15, but want to work through the jack plate height first. Thanks!!!