Toughness in pork loin can be caused by overcooking. To ensure the perfect texture and doneness, use a meat thermometer. For pork loin, the ideal temperature is 145 ℉. If your roast has been cooked above that temperature it could lead to tough or chewy meat. You should know that the pressure release process may take longer with thicker cuts of meat, so be sure to factor this into your cooking time.