Place chuck roast into a large slow cooker on medium or high heat. Sprinkle Ranch Seasoning Packet over top then pour Salsa over top as well.
Close slow cooker lid and let cook on medium or high for 5-6 hours, until beef is very tender and pulls apart easily with a fork.
Remove beef from slow cooker and drain liquid, do not discard. Shred beef, removing fat then place back into slow cooker. Pour 1/2-1 cup of liquid back into shredded beef and reduce setting to warm or low. Use beef for tacos and burritos.