Set a large sauté pan over medium heat. Add the sausage and break it into small pieces with a wooden spoon. Brown the sausage, stirring and breaking it into smaller pieces.
Once the sausage is cooked through, add the flour, thyme, salt, pepper, and garlic powder. Stir well to coat the sausage in flour, letting it absorb the grease. Stir and cook another 2 minutes.
Pour in 3 cups of milk. Stir and simmer to thicken the gravy. Once it is very thick and smooth, turn off the heat. If the gravy gets too thick, add another ½ cup of milk.