I had four pounds of chicken gizzards in the cooler in two bags cooked for 24 hours at 145F/63C. The seasoning was Mezzetta garlic and parmesan spread and Heinz 57 sauce. I reheated one of the bags in a hot pan then removed the gizzards, added some sriracha and corn starch to make a gravy.
The gizzards still had some texture but were not at all tough. The gravy had a wonderful, slightly sweet, slightly hot flavor. Very nice.