In a small bowl combine paprika, garlic powder, cumin, onion powder, adobo powder and chipotle powder. Rub evenly on both sides of beef; season with salt and pepper to taste. Wrap beef tightly in plastic wrap. Refrigerate at least 12 hours.
Coat a large slow cooker with nonstick cooking spray. Place onions in cooker; set aside.
In a large nonstick skillet heat oil over medium-high heat. Cut beef into two pieces; place in skillet. Cook each piece 2 to 3 minutes per side to brown.
Transfer beef to slow cooker; add tequila and lime juice. Cook on LOW 8 to 10 hours or until beef is fork-tender. Transfer beef to a platter; cover and keep warm.
For the sauce, skim fat from juices. Transfer juices and onions to a medium saucepan; bring to boiling. Reduce heat; cook, stirring occasionally, 10 to 15 minutes or until sauce thickens. Slice beef, and serve with sauce.