Place cubed beef in slow cooker and sprinkle evenly with lemon pepper. In a large bowl whisk together dry onion soup mix, cream of mushroom soup, and beef broth; pour over meat. Cover and cook on low for 8 hours.

Remove meat from crockpot with a slotted spoon, place in a bowl, and cover with foil. Set aside for now. In a large saucepan melt butter. Add flour and whisk well. Cook for about a minute. Whisk in the gravy/juices from the crockpot and heat until thickened and heated all the way through. Add in the set aside beef and simmer for a few minutes. Serve the beef tips and gravy over mashed potatoes, rice, or noodles.