Brown pork roast on all sides in a large skillet to remove excess fat. Make cuts in roast with a small knife and insert garlic slices; place in slow cooker and season with salt, pepper, and sage and thyme or poultry seasoning. Add broth and wine, if used. Cover and cook on low for 10 to 12 hours. Remove roast and skim excess fat from juices; combine flour with about 3 tablespoons cold water and whisk until smooth. Turn the slow cooker to high and stir in the flour mixture. Cook and stir until thickened (this may be done on the stovetop). Serve sauce over pork, with rice or potatoes.