Place roast in slow cooker. Combine remaining ingredients in a 2-cup measuring cup. Whisk together and pour over roast. Cook on low 10-12 hours for that fall-apart, insanely tender type of meat. (Or on high 6-8 hours.)
Prior to serving, ladle out about 1/4 cup of the juice in the crock pot and strain into a measuring cup. Whisk in 2 tsp cornstarch. Add in enough juice to make 1 cup. Microwave on high for 30 seconds and whisk again. Drizzle sauce over meat prior to serving.