Line the slow cooker with aluminum foil and set aside.
In a medium bowl, combine the ground beef, sausage, onion, garlic, egg, bread crumbs, tomato paste, Italian seasoning, Worcestershire sauce, salt and pepper until well blended. DO NOT OVER MIX.
Place the meatloaf mixture in the slow cooker and shape into an oval loaf shape (or round if your crockpot is round).
In a small bowl, whisk together the ketchup, brown sugar, vinegar and mustard.
Spoon half the glaze over the meatloaf to coat.
Place the lid on the slow cooker and cook for 3-4 hours on high or 6-7 hours on low. Check for doneness with an instant read thermometer. The meatloaf is done when it registers 160 degrees F.
Using the foil, lift the meatloaf out of the slow cooker and place on a baking sheet.
Transfer the meatloaf to the oven and broil on high for 3-4 minutes until the glaze begins to caramelize.
Remove the meatloaf from the oven and allow to rest for 10 minutes.