Seb mine vibrates when she is trimmed up to far as well, but I don't normally need to trim this high. Indeed trimming down is normally needed to help the boat on to the plane with a heavy load. Once going, trimming out a little so the prop is driving horizontal is all that is required, (although the exact position is guesswork because you can't see the drive).
Think the RN boats have a plate which says don't run out of water for more than five minutes or with the trim up.
Once she has had the oils changed and prop repaired just chuck her back in the water with the stern drive horizontal and drive her, she will be fine. These are big heavy ribs. They take alot of weight to upset the balance but also take forever to get on the plane. Part of the price you pay for a very seaworthy boat running on the red stuff instead of petrol.