What servo are you using for the ailerons? Someone mentioned this but not why. If you're using a lower powered servo than in the old original then it may not have enough torque to push the ailerons to full deflection. You can check the sticky threads here an in the Scratch Building forum for online calculators that tell you how much servo torque is needed to move a given size to a given angle. Punch in the numbers and see what they say. Don't forget to add the two sides up since you're using one servo for both. And finally you want some safety room on the torque value. You want the servo to be about twice as strong as what the calculator says the surfaces require. That way you're not risking having the servo operate near the stall point and you've got some speed allowance for when diving at higher than normal rates.