Place beef roast into slow cooker and add both soups.
Cook on high for 8-10 hours.
Preheat oven to low broil.
Remove roast from the slow cooker and place in a bowl or on a plate. Remove fat and shred.
Turn the slow cooker on warm. Ladle most of the liquid in the slow cooker into bowls for dipping, then put the shredded beef back into the slow cooker.
Place sub rolls onto baking sheets so that they are open and flat. Add shredded meat onto both sides of the sub roll. Place 2 slices of cheese over the shredded meat so it is almost entirely covered.
Broil on low until the cheese is melted. Serve with bowls of the slow cooker drippings to dip the sandwich into.