1. Process orange juice and next 8 ingredients in a blender until smooth.
2. Pierce roast with a sharp knife at 2-inch intervals. Place roast in a large zip-top plastic freezer bag; pour orange juice mixture over roast, turning to coat. Seal and chill at least 4 hours or up to 8 hours, turning occasionally.
3. Remove roast from marinade, reserving marinade. Place roast on a wire rack in an aluminum foil-lined roasting pan.
4. Bake at 450° for 30 minutes. Reduce oven temperature to 300°, and bake 4 more hours or until a meat thermometer inserted into thickest portion of roast registers 150°, basting with reserved marinade every 30 minutes during first 3 hours of baking time. Let roast stand 10 minutes before slicing.