I've got the same boat and know what you mean. Mine came with a 19P which was not enough hole shot for water sports. I went to a 17P and that made all the difference. My kids have gotten bigger, and bring more friends, so I now run a 16P. I can get on plane while towing a wakeboarder and tube at same time.
Some tips: You will learn how to keep a steady speed with practice. What you are probably experiencing is the aluminum blade bending under load and flexing back to original pitch as the load decreases. Make sure you have some weight in the bow. I tell my kids to sit in the front and let me know what the skiier is doing. I also keep my anchor under front left cushion. Trim tabs help. These are the things you have to do with a small engine. Good part of small boat is you can take them anywhere and enjoy two full weekends of watersports on a single 25 gallon tank of gas.