In a small bowl mix together flour steak seasoning, 1/2 tsp garlic salt and paprika.
Place stew meat in a large plastic storage bag. Sprinkle with the seasoned flour mixture. Seal the bag and shake until the meat is coated on all sides.
In a large skillet brown beef in a few drizzles of olive oil over medium-high heat on all sides. Work in batches, if needed. Arrange the meat onto the bottom of the slow cooker.
To the skillet add the Worcestershire sauce to deglaze the pan scraping any brown bits off the bottom. Add mushrooms, minced garlic, 1 teaspoon of steak seasoning, 1/2 teaspoon of dried thyme and cayenne, if using. Stir to combine.
Add 1/2-1 tsp each garlic salt and black pepper, adjusting the amount to your taste. Scrape any browned bits off the bottom of the pan then add 1 1/2 cups of beef stock. Mix well, remove pan from the heat.
Arrange the carrots, onion and celery over stew meat in slow cooker. Season raw veggies lightly with additional garlic salt, black pepper or steak seasoning.
Pour the broth and mushroom mixture over the top. Place lid firmly on top.
Cook on high for 1 hour then add the red potatoes. Continue to cook on high for an additional 4-5 hours or on low for 8-10. Stir well before serving.
Serve hot with rice, grits or cornbread, if desired.