Thanks Leisa for getting back and all your info you have supplied
Not sure if you seen my background, but I have a very extensive background with watercraft, this ski in my opinion is one of the best that Kawasaki has ever built, I was working there when this ski was developed and I have many hours on this model.
I believe that you have a problem with the hull, maybe not the hull itself but more with the placement of the sponsons, ride plate and it intake grate, maybe hull ? but something isn't right I can tell you that for sure, as this ski has never exhibited any weird hull problems. It could be something simple or not, however you purchased this ski about 2 months ago, this is a problem that you need to make Kawasaki Motors aware of, I'm not sure what the dealer did to make it better but there is usually not much done on a first service, maybe it was coincidental ? but for it to come back doesn't make sense, based on everything you said at this point I would lean more towards a power related issue, that is the only thing that will change, if it was something in the hull or a problem with a component on the bottom of the ski, I would suspect that it would be there all the time.
I believe that this is something that you should get Kawasaki involved with, they have a field service adviser in your area that would come to your dealer and that gets them involved.
Would you like some names and how about getting the process started, I would be glad to help you out ?