In small bowl, combine sherry, lemon juice, lime juice, vegetable oil, chili powder, cumin, salt, and black pepper. Place pork roast in plastic zipper bag. Pour mixture over pork. Marinate overnight in refrigerator.
When ready to cook, place roast in slow cooker crock. Sprinkle lemon pepper and lime zest over pork roast.
Cover and cook on LOW for 4 to 5 hours or HIGH for 2 to 3 hours until internal temperature reaches 145°F.