I have a 1998 Champion 181, with a 150 Mercury xr6. 23 tempest and no jackplate. Compression is perfect, but at WOT I am only seeing 5100 rpm at 55 mph on gps. I’ve seen similar setups hit 60 no problem. Would a jack plate help get the extra 4-500 rpm I’m needing, or do you think its in the motor?