In a large resealable plastic bag, combine the first seven ingredients; add pork. Seal bag and turn to coat; refrigerate for 8 hours or overnight.
Drain and discard marinade. Prepare grill for indirect heat. Moisten a paper towel with cooking oil; using long-handled tongs, lightly coat the grill rack. Grill pork, covered, over indirect medium-hot heat for 25-40 minutes or until a thermometer reads 160°. Let stand for 5 minutes before slicing.
In a small bowl, combine the mayonnaise, sour cream, lemon juice, sugar, ground mustard, Dijon mustard and horseradish. Serve pork on rolls with lettuce and mustard horseradish sauce. Yield: 6 servings.