Season the venison with garlic, grill seasoning, and chili powder. Place into a casserole dish, and pour in the beef broth. Cover the dish with a lid, and bake in preheated oven until the venison is tender, about 1 hour.
Meanwhile, melt the butter in a saucepan over medium heat. Once the butter begins to bubble, whisk in the flour. Cook while whisking constantly until the flour turns a golden yellow, and the bubbling slows, about 10 minutes.
When the venison has finished cooking, whisk 1 1/2 cups of the broth from the venison roast into the flour roux, and simmer for 15 minutes, whisking frequently. Add the venison to the gravy and serve.