I owned a Pilot 34 for five years but it had a Yanmar 370 hp single. The Cummins that you have was somewhat rare, but I hope you get a response.
Unless a mistake was made and Mainship installed the prop for the 3,300 Yanmar on your boat, I am surprised it is over propped and won't plane. Planning on mine was about 12+ kts. How fast will the engine turn, both in neutral and in gear? Your throttle stop may not be allowing full throttle. Also check that the turbine spins freely. It may be dragging and limiting power.
I am sure that if it is a new purchase then the bottom and prop should be clean. Otherwise.....
David