Arrange the sliced carrots, celery, and onion evenly at the base of your slow cooker.
Place the chicken thighs on top of the vegetables.
In a separate bowl, combine chicken stock, au jus mix, chicken gravy mix, garlic powder, onion powder, and black pepper, whisking until well blended.
Pour the prepared sauce over the chicken and vegetables in the slow cooker.
Cover and cook on high for 4 hours, or on low for 6 hours, until chicken is fully cooked through and tender.
Check that chicken has reached an internal temperature of 165 F and is easy to shred with a fork.
Garnish with fresh parsley if you like, and serve the pot roast warm alongside mashed potatoes, egg noodles, or rice.