Scatter the cut potatoes, carrots, and diced onion evenly across the bottom of your slow cooker.
In a mixing bowl, whisk together the warm water with the dry ranch dressing mix, brown gravy powder, and Italian seasoning packet until fully dissolved.
Position the beef roast directly atop the bed of vegetables inside the cooker. Gently pour the prepared liquid seasoning mixture over the meat, ensuring the top is fully coated.
Secure the lid and cook on the low setting for 7 to 8 hours, or on high for 4 to 5 hours, until the meat is fork-tender and easily pulled apart.
Serve warm, paired with the surrounding vegetables and pan juices, or with a homemade gravy if desired.