Mix flour, sugars, baking powder, baking soda, salt, and pumpkin pie spice in a large bowl. Set aside.
In a separate bowl, mix pumpkin, eggs, vanilla, and 1.5 cups of the buttermilk. Add to dry ingredients and whisk together. Add the remaining ½ cup buttermilk in small amounts until you reach the consistency you like. The batter should be quite thick, but slightly runny. If you like thinner pancakes, add more buttermilk until you reach the desired consistency.
Preheat a griddle on medium-high heat and lightly coat with butter.
Spoon batter onto the griddle, approximately ¼ cup per pancake, unless you want larger pancakes.
Cook for 5-6 minutes, until you see bubbles forming on the top, then gently flip and cook 1-2 minutes longer.
Serve topped with butter, maple syrup, and chopped pecans, if desired.