I have a 1987 Wellcraft 19 ft. 170 hp Mercruiser inboard. Slow getting out of the hole but feels like it runs good in top end but only getting 2200 - 2800 rpm's. Boat is rated 4200 - 4600 rpm. Not sure if tac is wrong, I have a 19 inch pitch prop on it. Could someone please tell me what they...