Bring chicken, water to cover, garlic powder, thyme, 1 1/2 tsp. salt, and 1/2 tsp. pepper to a boil in a Dutch oven over medium heat. Cover, reduce heat to medium-low, and simmer 1 hour. Remove chicken; reserve broth.
Cool chicken 30 minutes; skin, bone, and shred chicken. Skim fat from broth. Add chicken, bouillon, and remaining 1 tsp. salt and 1/4 tsp. pepper to broth. Return to a simmer.
Combine flour and poultry seasoning in a bowl. Cut in shortening and bacon drippings with a pastry blender until crumbly. Stir in milk. Turn dough out onto a lightly floured surface. Roll to 1/8-inch thickness; cut into 1-inch pieces.
Drop dumplings, a few at a time, into simmering broth, stirring gently. Cover and simmer, stirring often, 25 minutes. Garnish, if desired.
*2 tsp. butter plus 1/4 tsp. salt may be substituted.