In a large bowl, combine flour, baking soda, baking powder, brown sugar, cinnamon and salt.  Mix well.  In a separate bowl, combine pumpkin puree, eggs and vanilla.  Add pumpkin mixture to flour mixture until just combined.  Do not over mix.  Fold in chopped pecans. Spoon batter into lightly greased or lined muffin tin and fill to 2/3 full.  Bake in preheated oven at 350F for approximately 20 minutes or until golden and baked through.  Cool in muffin tins for 5 minutes until removing to wire racks to cool completely.