Place tenderloins in a large pan or dish. Combine soy sauce, bourbon, and sugar; stir well, and pour over tenderloins. Cover tightly and refrigerate several hours or overnight, turning meat several times. Drain, reserving marinade.
Place tenderloins on a greased rack in a shallow roasting pan. Insert meat thermometer in thickest part of meat. Bake at 325° for 1 hour and 15 minutes or until thermometer registers 170°. Baste every 15 minutes with marinade.
Transfer tenderloins to a warm serving platter. Cut into thin slices, and serve with Mustard Sauce.