In a large mixing bowl mix together prepared carrots, celery, potatoes & onions. Set aside.
In a large deep skillet heat 2 TBS olive oil over medium high heat until hot. Season top of roast with salt & black pepper. Place seasoning side down in hot skillet. Season top of roast with additional salt & black pepper.
Once bottom of roast is seared about 3-4 minutes and is golden brown with a crust on edges, flip over roast and sear an additional 3-4 minutes until golden. Turn on sides of roast to sear all the way around. Set aside.
In a medium bowl empty out the 3 packets (italian dressing mix, ranch seasoning mix, and brown gravy mix). Whisk together. Pour in 2 cups of beef broth while whisking and mix in minced garlic.
Spray the inside of a 6 quart slow cooker/crockpot with non-stick cooking spray. Place half of the mixed vegetables in the bottom of prepared crockpot. Place seared roast on top of vegetables. Place remaining mixed vegetables along the sides and top of roast.
Pour the 3 packet mixture all over the roast and vegetables in crockpot.
Place lid on crockpot and cook on high for 4-6 hours or on low for 8-10 hours until roast is fork tender and vegetables are cooked through and tender as well.
Remove roast from crockpot and place on a serving platter with the cooked vegetables.
Mix together 2 TBS cornstarch with 2 TBS cool water in a small dish and pour into the gravy in crockpot. Mix together until thickened. Pour gravy over the roast & vegetables on serving platter. Sprinkle with dried parsley. Enjoy.