If desired, sear the chuck roast in a skillet over medium-high heat for a few minutes on each side to enhance its flavor. Season the roast with salt, pepper, and garlic powder on both sides.
In the crockpot, layer the diced onions at the bottom. Place the seared chuck roast on top of the onions.
Add the sliced carrots, celery, and quartered potatoes around the roast.
Pour the beef broth into the crockpot, scraping up any brown bits from the skillet if you seared the meat. Add the ranch seasoning, brown gravy mix, and the remaining seasonings over the roast and vegetables.
Cover the crockpot and cook on low for 8-10 hours or on high for 4-6 hours, until the meat is tender and easily shreds.
Once cooked, remove the roast and vegetables from the crockpot. If desired, thicken the remaining liquid by mixing cornstarch with water to make a slurry, then adding it to the liquid and stirring until thickened.
Serve the roast with the gravy and vegetables.
When cooking a chuck roast in the crockpot, remember that the key to a tender result is low and slow cooking. If you're short on time or want to prepare the meal the night before, you can prep all the ingredients and store them in the fridge, then transfer them to the crockpot in the morning.
Additionally, feel free to experiment with different seasonings or vegetables based on your preferences!