Sandman1221 said..
First, you need to make sure you are balanced on the board in flight, that means your front and rear foot pressure is equal when in level flight. Imagine you are straddling a seesaw with the left seat level with the right seat when you have equal pressure on both feet, that is being balanced. So once you have the board setup for that, which involves the sail mast base position, then all you do to maintain a level flight is to gently rock back and forth as needed while sheeting the sail in and out. It takes a lot of balance and coordination. Right now you are probably shifting your weight back and forth without realizing it, and that is causing you to porpoise. If you have access to an Indo Board, that will help train you to balance your foot pressure while in flight since it replicates half of what is needed, the other half is sheeting in and out rapidly while in flight, and responding to gusts by sheeting in/out takes practice. I have very gusty conditions, and I can maintain a level flight, but it does take a lot of focus and very quick reflexes, and I do that without looking for the gusts, I just respond to the pressure on the sail. Sometimes I cannot respond fast enough and either go airborne (rarely) if I am too high to begin with, or drop straight down and land on the water with a bang in the case of a negative gust (very hard to respond to).

The kite foilers are using wind that is 90 feet up, and that wind is more stable since it has an unobstructed path. You are on the whitewater rapids of a narrow river, they are on a broad river that does not have major whitewater or rapids "most of the time".