Is the hydofoil sitting on the surface or just above it when the motor is trimmed back as when your running at a very fast cruise or above?
If not then your motor is probably too low. The hydrofoil will certainly help getting on the plane but once your traveling fast the foil can add drag and may even throw some spray if the motor is sitting too low as you cannot trim it back and high enough to clear the water flow.
The way I set my rigs up is best described as follows.
If your arm was long enough could you slide your flat hand along the water surface and the hydrofoil when your running fast on smooth water with the motor trimmed back?
With the optimum setup on a boat I had some time ago I could tow skiers etc in fresh water and turn really hard but the same boat in salt would break out on hard turns because it was sitting higher in the salt water.
Try lifting it and if you start to porpoise you may need to go down a hole.
Good luck with it.
Cheers
Chimo