Heat a large skillet over medium-high heat and stir in Italian sausage, ground beef, onion, and garlic. Cook and stir until the meat is crumbly, evenly browned, and no longer pink, about 15 minutes. Use a potato masher to mash and blend the meat mixture every few minutes. Drain and discard any excess grease.
Stir in diced tomatoes, tomato paste, tomato sauce, chicken broth, red wine, Italian seasoning, basil, salt, and black pepper.
Transfer the sauce to a slow cooker and cook on low for 6 to 8 hours.
