I have had the same trouble with pecan pie. My favorite recipe suggests 1 cup corn syrup as well as 2/3 cup sugar. I do not think the sugar can be substituted as it helps to solidify the pie. It is a delicious but temperamental pie and so the next time I am thinking of trying was of the similar but alternative recipes which suggest Maple syrup for corn, peanuts or other nuts instead of pecan, and one even suggests coconut oatmeal instead of the pecans. I don't think its the pecans fault but I'm thinking the coconut and oatmeal will absorb the liquid better. Also, my book suggests when checking for doneness, to gently shake the pie. If the liquid area in the center is smaller than a quarter, the pie is done.