t60 on a 17 twinvee

bought a used 17 twinvee with a t60 on it. can't run boat wide open, because water flows/boils up the the lower unit; splashes against the cowling on the powerhead; runs over the transom, and into the boat. at about 4200 rpm the problem lessens. i've run out of adjustment on the hydraulic trim, and think that the motor should "go down" further for proper boat performance. do i need a jack plate? this is getting to be an expensive project. all ideas appreciated.

[boats.net]

In most cases the motor would need to be higher but on that hull lowering it may help. I haven't rigged any 17 TwinVees and don't have any information on it, on the 19 the motor was mounted on 3rd hole.