Season the chuck roast lightly with black pepper.
Heat olive oil in a large skillet and sear the roast for 2 to 3 minutes per side until browned. This step is optional but adds extra flavor.
Place the sliced onion in the bottom of the slow cooker.
Arrange the potatoes and carrots around the onions.
Place the roast on top of the vegetables.
In a bowl, whisk together the beef broth, ranch seasoning, brown gravy mix, and Italian dressing seasoning until smooth.
Pour the mixture evenly over the roast.
Cover and cook on Low for 8 to 9 hours or High for 5 to 6 hours, until the beef is fall-apart tender.
Remove the roast and shred or slice it.
If you prefer a thicker gravy, whisk together the cornstarch and cold water, stir it into the slow cooker, cover, and cook on High for another 10 to 15 minutes.
Serve the roast with the potatoes, carrots, and plenty of the rich gravy.