Until the trim tabs arrive, try moving the battery forward, or adding some weight toward the front of the boat.

That should also help control the porpoising that occurs at high speed.

Another way to control this is to trim the outdrives down. This should lift the stern of the boat, and also help to put down force toward the bow of the boat.

Hmm, I just re read your post, and it sounds like you have been working all these options.[&:]