Transfer sauce and vegetables to slow cooker; place roast on top, pressing down to submerge in liquid as much as possible. Cook on high for 4-5 hours until fork tender.
To make gravy, remove 4 cups of sauce to saucepan; bring to a boil; stir in cornstarch/water mixture and cook until thickened, just a few minutes. Slice pot roast and serve with vegetables and gravy.