1 Cook the pork roast in a slow cooker, for the most tender roast. 2  Place the brown roast in the slow cooker for approximately 6 hours on low. 3  If your roast is extremely large, you may want to cut it into a few pieces. Cook the pork roast in the oven on 325 degrees Fahrenheit (163 degrees Celsius). 2  Cooking time will be 35 minutes per lb. (0.45kg) of meat. 3  A pork roast with the bone in will cook faster than a boneless roast.