You're trimmed up way too much. Way waaaay too much.
As mentioned, keep that rooster tail down at WOT, about the same height as the cowling. At lower speeds, trim down until the porpoising stops.
Same thing when cornering - trim down first. Not only will it stop the cavitation, but it will improve handling while turning.
From a dead stop, trim ALL the way down first before taking off. Then trim up slowly as speed increases. If it starts porpoising, trim back down or speed up.
Watch your RPM as you're wide open and trimming up. If it suddenly jumps up, you've trimmed up too much.
Hope that helps!