I demo'd a 16' Arima and noticed the same thing...this one was powered with a 70 YAMAHA 2stroke. It just did not want to come out of the hole with two people and gear.
I seriously doubt that the motor is your prob. That motor is probably the best 4stroke out there. EFI and proven technology make the more popular (or so it seems) motors seem like dinosaurs.
Arima is not the most efficient hull out there but I think you'll figure it out with trim.
Nice boat, good luck.
_________________________
If you leave things up to interpretation, there's no room to be right.