Tip* You can prep everything the night before and just keep it in the fridge until the morning. In the morning pop it in the slow cooker and cook on high for 8 hours.
Here's how to thicken your gravy:
In a small bowl or cup take 1/4 cup of cornstarch and 1/2 cup of cold water and stir together with a fork until there are no lumps. Add the cornstarch mixture to the slow cooker with the gravy and stir together. Let it cook for about 5 minutes and then either pour it over the roast or add it to a gravy boat.